Apparatus and method for calibrated testing of a vehicle electrical system

This specification discloses a vehicle electrical system tester which connects in parallel across the vehicle battery and the portion of the electrical system to be tested and measures voltage changes upon selective actuation of portions of the vehicle electrical system. Comparison of these measured voltages with predetermined values is used in evaluating whether the electrical system is operating properly. The method of testing using the apparatus includes measuring a first voltage level after connection of the apparatus, actuating a portion of the vehicle electrical system, measuring a second voltage level, calculating a voltage difference as a function of the first and second voltage levels, comparing the voltage difference to a predetermined voltage magnitude, and determining if the actuated portion of the electrical system is operating properly. Additional sensitivity can be achieved by establishing a third voltage level through the use of a calibration resistor.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
This invention relates to testing apparatus and, particularly, to an 
apparatus and method for testing vehicle components including the vehicle 
electrical system. 
(2) Prior Art 
A function of electrical testing equipment is to determine the existence 
and location of electrical system defects so that they can be corrected 
during manufacture and substantially reduce repair expenses. Among the 
known means of testing a motor vehicle manufacture is a relative elaborate 
system which provides an interface between moving vehicles and off line 
equipment including a computer, a card reader and a printer. Typically, 
such a system requires permanent modification of existing facility and is 
relatively expensive. 
Another prior art attempt at monitoring an electrical system of a car is 
taught in U.S. Pat. No. 3,783,378 issued to Mildner. The patent teaches 
the use of a battery adaptor which adds resistance to the vehicle 
electrical system. The battery cable is disconnected and the battery 
current is routed through the tester measurement circuitry. It would be 
desirable to eliminate the need for a special battery adapter. Further, it 
would also be desirable to reduce the hookup time required by such a 
special battery adapter. 
Although there are known means for testing various vehicle electrical 
system components there is still a need for a simple testing method which 
would reduce the amount of operator time required in comparison to any 
known prior art system. These are some of the problems this invention 
overcomes. 
SUMMARY OF THE INVENTION 
This invention recognizes that a portable vehicle electrical tester can be 
connected between the vehicle battery voltage and vehicle ground in 
parallel with the vehicle electrical system to be tested. The tester 
includes a voltage measuring means for measuring the voltage change due to 
actuation of a portion of the vehicle electrical system. Comparison means 
within the tester compare the voltage change detected by the voltage 
measuring means to a predetermined value to determine whether or not the 
actuated portion of the vehicle electrical system is functioning properly. 
In accordance with an embodiment of this invention, the method of testing 
includes the steps of connecting a voltage measuring means in parallel 
across the vehicle battery, measuring a first voltage, actuating a portion 
of the vehicle electrical system, measuring a second voltage level, 
calculating a voltage difference as a function of the first and second 
voltage levels, comparing the voltage difference to a predetermined 
voltage magnitude and determining if the actuated portion of the 
electrical system is operating properly. 
An apparatus in accordance with an embodiment of this invention is 
particularly advantageous to insure that the current draw and voltage 
measurement of all vehicle electrical systems are within specifications 
and that all required electrical optional equipment is present on the 
vehicle. In a preferred embodiment, the tester is a hand held device which 
contains a microcomputer, a printing head, a card reader and an analog 
digital voltage converter. The tester is powered through and makes its 
voltage measurements through the vehicle cigar lighter socket. It is the 
simplicity and portability which makes this tester particularly easy to 
use. Individual components are turned on and off by an operator, and the 
current drawn thereby is measured by detection of changes in battery 
voltage, taking the verify proper functioning of the vehicle air 
conditioning and heating system. The apparatus can include a display for 
directing the operator to proceed with specific test sequences. 
Additionally, an option data card supplied with the vehicle electrical 
system to be tested is used to indicate the absence or presence of 
individual components on the vehicle. The card can be read by the device 
and the appropriate test sequence initiated. When the card is unavailable, 
the operator can enter option data via a keyboard. Test results can be 
indicated to the operator by sounding a tone and by using the display. The 
operator can cause the system to retry a particular test. A message can be 
printed by the test set for adhesion to a record location found in the 
vehicle. A memory can be used to store the operating program and 
parameters. The memory and processing unit can be powered by internal 
batteries, while other power consuming equipment such as the printer and 
display can obtain power from the vehicle battery. The test set can 
further include a summary capability so that results pertaining to hourly 
or shift data, including defect rates are available. 
A repair buy-off or repair completion mode can be available for performing 
an individual test after repair of a detected problem. In this made, the 
operator enters the number of the failed device via the keyboard and the 
tester displays the name of the device to be retested. The operator 
activates the device which is then tested by the tester. If both the 
tester and the operator "ok" the test, the operator is requested to enter 
a 2 digit code via the keyboard which was written on the original reject 
print out by the repairman to describe the cause of the failure. For 
example, the repair code 1,1 would indicate "missing bulb". This is 
repeated until all failed devices are retested at which time a print out 
is obtained from the tester listing all items retested and their status. 
The repair codes are summarized on the shift report during transmission of 
defect summaries to the data terminal.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to FIG. 1, a vehicle electrical system tester 10 can be used for 
determining whether the electrical current draw of various vehicle 
electrical systems are within specifications and for providing a 
structured test sequence to be followed by quality control inspectors in 
an assembly plant. The test can be performed on a moving line or in test 
stalls with no physical connections between the vehicle and off-line 
equipment. Tester 10 is a hand held, stand alone, microcomputer controlled 
device which can be powered by, and makes voltage drop measurements 
through, a single connection to the vehicle battery at the cigar lighter 
socket or other appropriate location. The current being drawn by the 
device being tested can be calculated from the voltage drop and compared 
to limits in a memory 115 (FIG. 7). Results of the test, which can include 
defect rates, can be printed by tester 10. 
The electrical option content of the vehicle can be provided to tester 10 
by manual insertion of a specially punched, standard 80 column computer 
card 30, by another form of electrical data input or by having the 
operator answering yes or no via the keyboard as the tester displays all 
possible vehicle electrical options. After such information is provided, 
tester 10 can provide prompting information to guide a quality control 
inspector through the required tests by sequentially displaying 
instructions on a light emitting diode, alpha numeric visual display 13. 
As the inspector activates the various vehicle electrical systems, the 
tester will automatically determine the current draw and compare it to 
acceptance limits stored in memory 115. Upon completion of the test 
sequence, the inspection results can be printed by tester 10 while it is 
still connected to the vehicle. In addition to the hand held testers 10, 
there can be an off-line programmable data terminal or analyzing means 
100, such as shown in FIG. 6, used for storing data and printing defect 
summaries. 
Vehicle electrical tester 10 is a generally rectangular box having a 
keyboard 11 on the front thereof having a plurality of buttons 12 
indicating number entries for tester 10. Tester 10 includes a cable 20 
having connected thereto a vehicle connector assembly 21 for connection to 
the vehicle at a point such as the cigar lighter socket. The front face of 
tester 10 includes three button lights 14a, 14b and 14c which indicate 
whether the result of the test is satisfactory (OK), the voltage recorded 
is below the acceptable limit (LO), or the voltage recorded is above the 
permissible limit (Hi), respectively. A cable 15 extends from tester 10 to 
a control handle 17 having control buttons 16a, 16b, 16c, for use by a 
test operator to enter the result of any test which has a visual result to 
be observed by the test operator. For example, button 16a indicates 
satisfactory test completion (OK), button 16b indicates rejection (REJ), 
and button 16c indicates a retry of a certain test (RTY). Control handle 
17 also includes an air flow port 18 wherein there is contained a 
temperature sensing device 19 which changes electrical characteristics in 
response to the temperature of the air flow from a vehicle air 
conditioner. Tester 10 further includes a slot 22 for receiving computer 
card 30 containing option information and a printer for providing a 
printed output 23 of the electrical system test results for a given 
vehicle. A handle 52 is attached to a case 53 for carrying tester 10. 
Connector assembly 21 is electrically connected to handle 52 to provide a 
discharge path for both tester 10 and an operator holding handle 52. 
The format of option data computer card 30 utilizes punched holes in a 
column and line matrix which can be read by a built-in card reader having 
a card guide, three or four photocells with light sources and the software 
to interpret the information. Each column represents a particular option 
and is punched either true on one line or false on another line. Since 
each column is punched, punches in other lines can be correlated with the 
appropriate columns as the operator manually inserts and then removes the 
card. The card reader can be designed so that the operator must fully 
insert the card and then fully remove the card with only one change in 
direction of motion, in order for the information from the card to be 
accepted. 
In some applications it may be desirable to replace or supplement the card 
reading capability of tester 10 with a bar code reading capability. For 
example, tester 10 can have the capability of reading in the vehicle 
serial number and option content in the vehicle electrical system by means 
of a bar coded label. Tester 10 can then be used for reading and verifying 
that the proper vehicle components have been assembled. 
Vehicle electrical system tester 10 operates by measuring battery voltage 
fluctuations to check vehicle electrical systems. Additionally, tester 10 
can accept an input from the operator who has conducted a visual 
inspection and an electrical input from a transducer used to measure 
various physical properties. Advantageously, the voltage reading made by 
tester 10 are actually the average of a minimum of 32 discrete voltage 
measurements to eliminate the effects of noise. Tester 10 can perform the 
following seven different test types to evaluate the performance of a 
vehicle electrical system. 
First, referring to FIG. 3, there is the measurement of an absolute voltage 
level and comparison of that level to a predetermined value. For example, 
in order to verify that a vehicle battery 24 is sufficiently charged, 
tester 10 measures the DC voltage at a cigar lighter socket 25 and adds a 
correction factor to compensate for voltage drop in the vehicle wiring, 
typically 0.2 volts. 
Second, there is the measurement of a voltage change. For example, in a 
full load alternator test, to assure that the alternator has sufficient 
output, the engine is run at 2000 rpm with the headlamps and high blower 
turned on. Tester 10 then measures the voltage across the vehicle battery 
24 and assures that the voltage increase is by at least 0.2 volts but not 
more than 3 volts over the voltage present prior to starting the engine. A 
no-load alternator test is similar to the full load test except that the 
headlamps and blower are turned off and the tester assures that the 
voltage is between 12 and 15.5 volts. 
Third, there is a voltage change measurement in response to the resistance 
change of a transducer. For example, an air conditioning cooling test is 
done by holding temperature sensing device 19, such as a thermistor, in 
front of an air conditioner register. To verify that the air conditioning 
is cooling, tester 10 records a voltage level representing the initial 
temperature and continues to sample until a reading is obtained which is 
approximately 3.degree. F. below the recorded reading. The concept of 
using resistor variation can be expanded to measure other physical 
properties of the vehicle by using different transducers. For example, 
transducers may measure vacuum, torque, paint thickness, color, lamp 
intensity, magnetic flux of spot welds, direct current, etc. 
Fourth, a visual test by the inspector requires no automatic inputs by 
tester 10. The inspector visually inspects and then accepts or rejects the 
test being displayed prior to continuing on to the next test. Further, in 
a preferred mode of operation of tester 10, all of the tests performed by 
tester 10 require a verifying input from the operator prior to going on to 
the next test. 
Fifth, a calibrated current measurement test can be used on portions of a 
vehicle electrical system which are substantially resistive loads, such as 
lamps and heated backlights. Referring to FIG. 2, a typical sequence 
during a calibrated current measurement test includes displaying a message 
on visual display 13 such as "brake lamps, on and off" and taking voltage 
readings. When a portion of the vehicle electrical system is turned on, 
tester 10 senses the turn on via lower voltage readings. The voltage 
reading before system turn on is recorded. After delaying a programmable 
time period to allow turn on transients to settle out, a second voltage is 
recorded and a calibration resistor is momentarily turned on and the 
resulting voltage is recorded. The obtained voltage readings are used to 
calculate current drawn by the vehicle electrical system and verify that 
it is within limits. All the voltage readings are advantageously made by 
taking a programmable number of voltage readings and determining the 
average of the readings. 
Sixth, a non-calibrated current measurement test is used to test systems 
such as motors and turn indicator signals where it is not practical to use 
the calibration resistor discussed above due to the large amount of 
electrical noise generated by these systems. Voltage readings are made 
before and after the actuation of a portion of the electrical system. The 
difference between these two voltage readings is then scaled to provide a 
measurement of current draw. Different scaling factors are used depending 
upon the size of the vehicle's battery. For example, this type of test 
includes measurement of the average current as a power window is fully 
lowered and then raised. 
Seventh, a ripple test is used to verify that various vehicle warning 
buzzers are operating. Tester 10 performs this test by filtering out the 
DC voltage and all frequencies outside of a 50 to 700 Hz band, performing 
a full wave rectification of the ripple and by then measuring the average 
value of the resulting ripple. This test can also be used for motors. 
In a typical application, it is advantageous to have the voltage 
measurements used to determine acceptable battery voltage and alternator 
charging voltages to be accurate to within plus and minus 1 percent. 
Further, all voltages can be measured to a resolution of .+-.2.5 
millivolts with an absolute accuracy of .+-.12 millivolts using a 12 bit 
analog to digital converter with a resolution time of 150 microseconds. A 
typical test sequence is estimated to require from about 41/2 minutes to 
about 6 minutes per vehicle depending upon the option content of the 
vehicle. Each of the hand held testers 10 can be connected to analyzing 
means 100 approximately once per hour for transferring data and printing 
defect summaries. 
Referring to FIGS. 2 and 3, the calculation of a current, I, which is 
indicative of the resistance of the portion of the electrical system to be 
tested is computed using the values of voltage measured during the 
calibrated current test as well as the magnitude of the various 
resistances in the circuit. Voltage V.sub.1 is the level measured before 
actuation of the portion of the electrical system to be measured, level 
V.sub.2 is the voltage level measured during the time calibration resistor 
31 is connected by a switch 32 across vehicle battery 24. A voltage level 
V.sub.3 is measured when switch 32 is opened and a switch 33, connecting a 
load resistor 34 across battery 24, is closed. A resistor 35 is the 
internal resistance of battery 24 and is typically approximately equal to 
about 0.012 ohms. A resistor 36 is the wiring resistance and is typically 
equal to about 0.01 ohms. Calibration resistor 31 is typically about 6 
ohms. A resistor 38 and a resistor 40 are the cigar lighter socket contact 
resistances and each equals approximately 0.005 ohms. An analog to digital 
converter 26 has an input resistance of about 10 mega ohms. Resistance 39 
and resistance 37 are also the cigar lighter contact resistances and have 
a similar value to resistances 38 and 40, that is 0.005 ohms. Resistances 
37, 38, 39 and 40 are somewhat erratic due to the poor contact 
characteristics of the chrome plating of the interior of the cigar lighter 
socket. In solving the circuit shown in FIG. 3, load current I.sub.L is 
found to be equal to: 
##EQU1## 
The terms "1.63" and "13.63" have been found to vary as a function of the 
characteristics of the power supply for the tester, e.g., the vehicle 
battery. 
Referring to FIG. 2, a dotted outline 42 indicates that calibration 
resistor 31 can be turned on before switch 33 is closed and the portion of 
the electrical system to be tested is connected across vehicle battery 24. 
In this case, the level of the bottom portion of dotted outline 42 is 
denoted as V.sub.4. The current I.sub.L through resistor 34 is found to be 
equal to: 
EQU V.sub.1 -V.sub.3 /R.sub.36 +R.sub.35 
Voltage V.sub.1 is equal to the vehicle battery voltage E.sub.b and voltage 
V.sub.3 is known. In solving for resistors 35 and 36 using a typical 
single circuit cigar lighter socket connector, the converter 26 measures 
the voltage V.sub.sc as shown in FIG. 3. Therefore: 
##EQU2## 
Since the term R.sub.37 +R.sub.39 can be up to 0.01 ohms, approximately a 
50% error may occur. In solving for R.sub.36 +R.sub.35 using the proposed 
dual circuit cigar lighter socket connector, the following results: 
##EQU3## 
The error involved is 
EQU (R.sub.37 +R.sub.39)/R.sub.31 
which is approximately 0.01 divided by 6 or 0.2%. This is relatively 
insignificant. 
A vehicle battery is not necessarily 12 volts and the actual current may 
vary from the current associated with a standard 12 volts. To get the 
current at a standard 12 volts we multiply the actual current by the ratio 
12 divided by V.sub.1. Further, the above mentioned 1.63 factor has been 
derived to be typically of automobile electrical systems which has been 
tested. 
The following is a listing of items which can be inspected by an operator 
and whether they use a visual check, an electrical check or a combination 
of both visual and electrical checks. 
TABLE I 
______________________________________ 
Elec- 
Visual Visual & trical 
Check Electri- Check 
COMPONENTS INSPECTED 
Only cal Check Only 
______________________________________ 
Illuminated Entry x x 
Electrical Door Lock x 
Park Lamp x 
Cluster Lights x 
Floor PRNDL Light x 
(Transmission Indicator Light) 
Radio Light x 
Ash Tray Light x 
Clock Function and Light 
x 
Headlamp Key Warning 
x x 
Headlamps Low Beam x 
Head Lamps High Beam x 
Power Seats x 
Brake Lamp x 
Horn Standard x 
Horn Deluxe x 
Harzard Flashers x 
Cigar Lighter x 
Console Light x 
Dome/Map Lights x 
Visor Lights x 
Glove Box Light x 
Seat Belt Buzzer and Light x 
Engine Alternator Light Gages 
x 
Park Brake Warning Light 
x 
Turn Signals x 
Cornering Lights x 
Wiper Washer x 
Door Jam Switches x 
Door Ajar Lights x 
Key Warning Buzzer x 
Automatic Seat Belt Release 
x 
Power Windows x 
Back-up Lights x 
Rear Wiper Washer x 
Radio Speakers x 
CB Microphone Plug x 
Deck Release x 
Heated Back Light x 
Rear Defogger x 
Air Conditioner Heater Blower 
x 
Air Conditioner Cooling x 
Brake Warning Light 
x 
Starter x 
Climate Control Modes 
x 
Full Load Alternator x 
No Load Alternator x 
Battery x 
Radio Antenna x 
______________________________________ 
Tester 10 is connected to the vehicle electrical system by means of a 
vehicle connector 21, which is the subject matter of a copending 
application entitled "Connector Plug for Vehicle Electrical Tester", with 
the same inventor and assignee as this application, the disclosures of 
which being incorporated by reference herein. A special connector assembly 
21 having a dual connection is required because, to obtain accurate 
voltage measurement of the vehicle electrical system through a cigar 
lighter socket, the voltage drop at the connection contact points must be 
very small. Typically, the materials used in present day cigar lighter 
sockets do not provide for very low contact resistance. Therefore, it is 
particularly advantageous to use a dual circuit cigar lighter connector. 
One circuit is used for connecting sensitive measurement data and the 
other circuit is used for supplying power to tester 10. The principle of 
using dual circuits also applies to measurements taken at any point in the 
vehicle electrical system where battery voltage and ground are available. 
For example, this includes the battery terminal, fuse block, lamp, 
sockets, diagnostic vehicle electrical connectors and on-board vehicle 
microcomputers. If a vehicle does not have a cigar lighter socket, tester 
10 can be connected to the wire which would normally power the cigar 
lighter. 
Referring to FIG. 7, a microcomputer 111 includes a comparison means for 
comparing voltages and is connected to a memory means 115 and to a filter 
and rectifying means 112 through a voltage measuring means 113, and a 
multiplexing means 125 which selects an input line to be used. Voltage 
level measured by voltage measuring means 113 are compared in the 
comparison means of microcomputer means 111 to predetermined values 
received from memory means 115. As further discussed later, the 
predetermined levels and memory means 115 can be altered by microcomputer 
111. Microcomputer 111 also controls a coupled display 13 thereby 
providing prompting information to the operator. Key pad 11 is also 
connected to microcomputer 111 and provides a manual information input 
into microcomputer 111 which can then be stored, if desired, in memory 
means 115. A printer 122 is also connected to microcomputer 111 and is 
actuated by microcomputer 111 and prints out information supplied to 
printer 122 by microcomputer 111. Microcomputer means 111 is also 
connected to a reader 123 such as a card reader, and indicator means 126, 
such as lights and buzzers, and an analyzing means 100. Connector means 21 
is coupled to microcomputer means through a calibrated load means 127 and 
to multiplexing means 125 both through a noise filter 128 and filter and 
rectifying means 112. A temperature transponder means 129 is connected to 
multiplexing means 125. 
The software of tester 10 is designed to maintain a running means and 
standard deviation for each of the various tests, such as those described 
above, performed on the vehicle. Acceptance upper and lower limits are 
implemented by setting two parameters which establish within tester 10 the 
number of allowable standard deviations from the mean. Thus, tester 10 
includes an automatic limit concept. 
Current limits are statistically developed and used by tester 10 unless 
over-riden by manual input of limits. Tester 10 develops a current draw 
average and standard deviation for each test and is to accept or reject 
based on limits determined by average current plus "X" standard deviations 
and average current minus "Y" standard deviations. "X" and "Y" are to be 
programmable parameters and are typically equal to about three. In order 
for a new current value to be used in developing limits during normal 
operation, the device which is drawing the current must be within 
previously developed limits. The current average can be developed by 
programming the following equation: 
EQU IA(L)=IA(L)+I-IA/N(L) 
where 
IA(L) IS the current average for test "L" 
I is latest current measurement 
N(L) is number of samples in current average. 
The standard deviation can be developed using the following equation: 
##EQU4## 
where (L) is the standard deviation for test "L". During development of 
limits for a device, the first ten current readings which are greater than 
zero and which are visually accepted are used for limit development. After 
this, the limits are operational and N(L) is allowed to increase to 
approximately 1,000. N(L) is then held constant as new current readings 
are continuously entered into the above equations. This will allow the 
testers limits to be slowly corrected to the actual current averages and 
standard deviations. For example, if the actual current average suddenly 
shifts one percent due to changes in the manufacturing techniques of a 
device, the testers's average will change approximately 0.7 percent during 
the first week and an additional 0.2 percent during the second week. 
If a large acceptable change occurs in the actual current and standard 
deviation, N(L) is to be set to zero and new limits developed. Should it 
be found desirable to have fixed limits for any tests, provisions are 
provided by which the tester's limits can be printed out and used for 
reference while programming fixed limits. 
Referring to FIG. 6, an analyzing means 100 includes a printer output 101, 
a cathode ray tube output 102, and a charging unit 103. Portable tester 10 
can be coupled to charging unit 103 to recharge internal batteries. 
Additionally, portable tester 10 can be coupled to analyzer 100 to both 
receive and transmit data. That is, instructions stored in analyzer 100 
can be transmitted to tester 10 to govern the operation of tester 10. Data 
stored in tester 10 during operation, can be transmitted back to analyzer 
100 for analysis and print-out. Analyzer 100 further includes a remote 
input 105, such as a telephone modem, for receiving instructions to be 
transmitted to tester 10 so that the instructions in analyzer 100 can be 
changed from a remote location. 
Typical components are a Texas Instrument TI-742 for the data terminal, a 
Texas Instrument Model 810 for the remote printer, and a modem 
manufactured by Vadic Corporation, such as the VA-1240K, for communication 
among the TI-742, the remote printers, the visual displays and the 
VA-1205-D auto answer. Such a connection provides for communication 
between a central and a remote location to permit updating of program 
tapes. The central processor, the above mentioned TI-742 includes a 
display screen for providing prompting for the operator. For example, the 
first display typically requires the operator to establish a set of 
initial conditions so that there can be a segregation between previous 
data and new data. 
OPERATION 
The basic test sequence using tester 10 includes connecting tester 10 to 
the cigar lighter socket by means of vehicle connector assembly 21. Option 
data computer card 30, containing information about the vehicle electrical 
system, is inserted into an internal reader 123 of tester 10. The 
operation of inserting and removing computer card 30 reads the material 
into tester 10 and stores it therein. Once computer card 30 is removed 
from tester 10 it can again be attached to the vehicle. If desired, for 
reasons such as unavailability of option data computer card 30, the 
operator can manually enter the option and model information by use of key 
pad 12 in response to true and false queries presented by tester 10 at 
visual display 13. 
After the option information has been entered into tester 10, visual 
display 13 displays the first electrical device to be tested by the 
operator and prompts the operator to take the action required to test the 
device, for example, turn on the dome lamp. When a significant voltage 
change is transmitted to tester 10 through cable 20, tester 10 waits a 
predetermined time period and then takes a series of readings over a 
predetermined time period to find the average voltage change. Tester 10 
then switches in (using a switch 32) a calibrated resistor 31 (FIG. 3) and 
measures the resulting voltage drop in order to calculate the internal 
resistance of battery 24 and wiring system shown in FIG. 3. Using the 
values found when the calibration resistor is switched in, the current 
draws are calculated and compared to those limits for the test being 
performed. Tester 10 displays the appropriate words "pass", "low", or 
"high" and, if desired, produces an audio tone which is different for each 
of the different messages. 
After tester 10 has evaluated the test to be performed, the operator turns 
off the electrical device being tested and pushes either the "visually 
OK", "visually reject" or "retry" button. If the "retry" button is pushed, 
the step of inserting calibrated resistor 31 and performing the task on 
the portion of the electrical system being tested is repeated. If the 
"visually ok" or "reject" button is pushed, the tester records the results 
and displays the next test to be performed. Under normal test, the 
operator will proceed through the testing sequence by turning the device 
on, listening to the buzzer which indicate the test results, turn the 
device off and enter his visual inspection results. 
After the operator has sequenced through all of the tests to be performed, 
such as those listed in Table I above, an "end test" message will be 
displayed by the tester. If all the items tested were visually and 
electrically accepted, the tester will print the vehicle serial number and 
print a message such as "all electrical items are ok". If failures have 
been encountered, the tester will print the serial number and a message 
such as "brake lights low, dome light open." The operator tears off the 
message which has exited from printer 23 of the tester 10. Typically, the 
message is attached to the vehicle for further action. The operator can 
then disconnect and remove tester 10 from the vehicle. During some tests 
it may be advantageous for the inspector to leave the interior of the 
vehicle to do a visual examination. For example, a walk around visual 
check of the vehicle exterior illumination such as, for example, cornering 
lamps, flasher bulbs, hood light, deck light, and all side marker and park 
lamp bulbs can be visually verified as functional or not. 
Reprogramming of tester 10 can be accomplished by several methods. For 
example, a magnetic tape cassette of the program changes can be made at a 
central location and mailed to the production facility where the vehicle 
electrical systems are being tested. A data terminal can then be used to 
transmit the program changes to the tester when the tester is connected to 
the data terminal. Alternatively, program changes can be typed into the 
data terminal directly, recorded on a magnetic tape and entered into the 
tester. 
In a situation where there is no computer card 30 and the operator is 
inserting the information itself, tester 10 supplies prompting 
information. For example, tester 10 will display information about the 
vehicle electrical systems and the operator must note the information 
displayed and verify its accuracy. If the displayed information is not 
correct, the inspector can press button 16b or 16c and manually enter the 
correct information. 
After this initial entry of this information, a typical signal displayed by 
tester 10 will read "turn off all electrical items". This is a reminder to 
the inspector to turn off any electrical devices which may have been 
previous left on in order to proceed with the next test. The inspector can 
sequence the next instruction from tester 10 by pressing button 16a 
indicating a "visual ok". 
The general format of the display at visual display 13 can be that the top 
line is the name of the device to be tested and the bottom line will 
contain a general instruction on how to activate the device. In some 
cases, the inspector may wish to have tester 10 reexamine the device which 
has failed or passed. To accomplish this, button 16c for retry can be 
actuated. A typical printed output format for tester 10 is shown in FIG. 
4. 
Periodically, for example approximately every hour, the operator connects 
tester 10 to a line data terminal or analyzing means 100 and detect data 
is automatically transmitted to the analyzing means. Analyzing means 100, 
will automatically print out the defects summary for the last hour when 
all of the testers (e.g., 5 or 6) in use have transmitted their defect 
tables. At the end of another period of time, such as the end of a shift, 
the operators can connect each of the testers to the off line data 
terminal, one at a time for transmission of the defect tables. The data 
terminal will print out the defects summary for the entire shift. At the 
same time, the data terminal can record the defect summary on a magnetic 
tape cassette for permanent record. 
Vehicle electrical systems which have been previously rejected by tester 10 
and have been repaired can be retested. FIG. 5 shows a block diagram of a 
typical sequence for correcting a fault. The inspector connects tester 10 
to the cigar lighter socket and sequences tester 10 to the test to be 
performed. This causes the name of the test to be displayed on visual 
display 13 and select the acceptable limits for the test to be performed. 
The inspector performs the specified test and observes the display for the 
results. If the test system results are electrically and visually 
satisfactory, the inspector will push the "visually ok" button 16a. The 
tester will then send out a message such as "headlamps passed retest" will 
be printed out. This procedure is repeated until all repairs are retested. 
The inspector then tears off the written message from tester 10 and 
attaches it to the vehicle electrical system. 
In addition to the above described selective retest operation, wherein the 
inspector checks a small number of items by entering in their device code 
and executing a test on that device, a complete retest can be done. 
Typically a complete retest would not be used where only one or two 
defects were found. A complete retest is similar to a normal test in that 
when the complete retest operation is finished visual display 13 displays 
end of test and printer 23 issues a report on the test. 
Various modifications and variations will no doubt occur to those skilled 
in the various art to which this invention pertains. For example, the 
particular physical configuration of the tester may be varied from that 
described herein. These and all other variations which basically rely on 
the teachings through this disclosure has advanced the art are properly 
considered within the scope of this invention.