Towed vehicle electrical system wiring device

The control circuit of a towing vehicle is coupled to the signal lights of a towed vehicle to allow the signal lights of the towed vehicle to be controlled by the towing vehicle. The coupling itself is conveniently located and readily made or broken. A signal blocking circuit prevents signals from the towing vehicle from affecting control circuitry in the towed vehicle.

TECHNICAL FIELD 
This invention relates generally to wiring harnesses as used with towed 
vehicles, and more particularly to protection circuitry for electrical 
components used in the towed vehicle. 
BACKGROUND ART 
Vehicles such as automobiles generally include their own locomotion 
capability. This locomotion capability in modern vehicles often includes 
an internal combustion engine and an appropriate control mechanism. The 
control mechanism will often include a microprocessor or microcomputer. In 
fact, many automobiles now include a plurality of microprocessors to 
enable optimum and efficient control of a variety of vehicle functions. 
These microprocessors receive input signals and provide control signals 
through conductors that are properly disposed throughout the vehicle. 
From time to time, it becomes desirable or necessary to tow such a vehicle. 
In this mode, a towing vehicle provides the locomotion and the towed 
vehicle moves in passive conjunction therewith. Since the towed vehicle 
will usually occlude the tail mounted signal lights (such as brake lights 
and turn signal indicators) of the towing vehicle (as viewed from behind), 
provision must be made to ensure that appropriate signal lights are 
provided at the rear of the towed vehicle. 
Pursuant to one prior art approach, signal lights can be electrically 
connected to the appropriate control lines of the towing vehicle and then 
temporarily connected to the exterior of the towed vehicle. This approach 
involves significant cost for the exterior mounted lights, inconvenience, 
and risk to the exterior finish of the towed vehicle. 
Pursuant to another prior art approach, the signal lights of the towed 
vehicle itself are electrically connected to the appropriate control lines 
of the towing vehicle, such that the signals lights of the towed vehicle 
switch on and off in direct response to the control signals of the towing 
vehicle. Though avoiding many of the problems of the earlier prior art 
approach noted above, this solution does give rise to other problems as 
well. 
For example, intercoupling the control lines of the towing vehicle with the 
control lines of the towed vehicle can be tedious and time consuming, 
partiuclarly if the operator needs to make and break this coupling on a 
repeated basis. Also, the control signals initiated by the towing vehicle 
(or other signals present on the control lines, such as voltage or current 
spikes) may damage the electronic control devices (such as 
microprocessors) of the towed vehicle. 
A need therefor exists for a towed vehicle electrical system wiring device 
that will allow relatively rapid and conveneient coupling to be effected 
between a towed vehicle and a towing vehicle on a repetitive basis. This 
device should also preferably additionally function to protect the 
electronic control devices of the towed vehicles. 
SUMMARY OF THE INVENTION 
These needs and others are substantially met through provision of the towed 
vehicle electrical system wiring device that is decribed herein. This 
device includes generally two inputs. One input is for coupling to the 
control line output ports of the electronic control devices of the towed 
vehicle. The remaining input is for temporarily coupling to the control 
line output ports of the electronic control devices of a towing vehicle. 
The device also includes an output that couples to the rear signal lights 
(such as the brake lights and turn signal lights) of the towed vehicle. 
In one embodiment, signal blocking devices are included to prevent control 
signals (or any other signals) provided by the towing vehicle from being 
presented to the control devices of the towed vehicle. Instead, the 
control signals from the towing vehicle are only allowed access to the 
signal lights of the towed vehicle, thereby protecting the control devices 
of the towed vehicle. 
In another embodiment, the temporary coupling between the control signal 
inputs from the towing vehicle and the second input of the device can be 
conveniently located in the cabin of the towed vehicle. Such convenient 
location allows relatively rapid access to the coupling by the operator, 
and thereby allows the towed vehicle to be readied for towing in a 
relatively simple manner.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawing, the invention can be seen in FIG. 1 as 
generally depicted by the numberal 100. The invention operates in 
conjunction with the control circuit (101) of the towed vehicle and the 
rear signal lights (102 and 103). In particular, the control circuit (101) 
provides control signals in a known manner to the rear right-side brake 
and turn signal lights (102), the rear left-side brake and turn signal 
lights (103), and the rear license plate light (109). (The precise 
coupling between the control circuit and signal lights will vary, of 
course, from vehicle to vehicle in accordance with the particular control 
scheme used; for example, some vehicles use only a single light on the 
left side and a single light on the right side and do not provide separate 
brake and turn signal lights. The teachings of this invention are equally 
applicable to such alternatively configured vehicles.) 
This coupling between the towed vehicle control circuit (101) and the rear 
signal lights (102 and 103) comprises a permanent coupling in this 
embodiment, although in an appropriate embodiment the coupling could be 
made temporary if desired, as through use of a plug. 
The invention also includes a plug (104) that allows the control lines to 
the signal lights to be coupled to the control circuit of a towing vehicle 
(105). In this embodiment, a breakable coupling is used to allow the 
connection to be readily made or broken. Preferably, the breakable 
coupling is conveniently located; for example, the coupling may be 
affixed, through the use of Velcro, inside the passenger cabin of the 
towed vehicle, underneath the glove box. So positioned, the coupling can 
be easily accessed to allow the coupling to be made or broken. 
If desired, a second coupling (106) can also be used. This second coupling 
may be conveniently located on the exterior of the towed vehicle. This 
allows the control lines from the towing vehicle to be readily connected 
to the towed vehicle. 
This embodiment also includes signal blocking devices (107). In particular, 
a diode (108) can be serially coupled with each control line from the 
towed vehicle control circuit (101). So configured, control signals from 
the towed vehicle control circuit (101) pass unobstructed to the signal 
lights (102 and 103). Control signals from the towing vehicle control 
circuit (105), however, are prevented from entering the towed vehicle 
control circuit (101). In this way, the delicate and sensitive components 
of the towed vehicle control circuit (101) are protected from both the 
control signals provided by the towing vehicle control circuit (105) and 
other potentially harmful signals that may appear on the control lines. 
The value of the diodes (108) is selected to accomodate expected signal 
levels. For example, control signals intended for the turn signals and the 
license plate light may require use of a 1 ampere diode, whereas control 
signals intended for use with the brake lights may require use of a 3 
ampere diode. 
A vehicle equipped with this invention can be readily configured for towing 
with a minimum of time and effort required. Further, a vehicle so equipped 
will allow the control signals provided by the towing vehicle to control 
the rear signal lights of the towed vehicle, while simultaneously 
protecting the control circuitry of the towed vehicle from the signals 
provided by the towing vehicle. 
Those skilled in the art will appreciate that various modifications can be 
made to the described device without departing from the spirit and scope 
of the invention.