Date: 201910
Local time of day: 1801-2400
Flight conditions: VMC
Light: Dusk
Aircraft: B767-300 and 300 ER
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Cruise
Airspace: Class A ZZZ
ATC / advisory: Center ZZZ
Aircraft component: Indicating and Warning - Lighting Systems
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: Pilot Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Troubleshooting
Second reporter function: First Officer; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Maintenance
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Diverted; General Flight Cancelled / Delayed; General Maintenance Action
Contributing factors: Procedure; Manuals; Incorrect / Not Installed / Unavailable Part; Aircraft; Human Factors
Primary problem: Incorrect / Not Installed / Unavailable Part

Narrative: Airplane had just come out of an A Check. Departed ZZZ uneventfully. When we got to cruise; we turned on the light override in the cockpit. A few minutes later; I realized that I had both Bus a Tie ISLN lights; both Gen Drive lights and all the window heat lights displayed. There were no associated EICAS messages for any of these. We were over the water; so we got a clearance towards land and started the APU. I had the First Officer fly and do the radios while I contacted company on SATCOM. I spoke with dispatch; Maintenance Control and a duty pilot. No chief pilots were available. I looked through the QRH; but following it; would have directed us to disconnect the generator drives. That wasn't what we wanted and would have been detrimental in this instance so I decided that since everything seemed to be working; I wouldn't follow it. The decision was made to divert. We set up to land in ZZZ1. [We advised ATC]. On the descent when we turned the lights override off; we realized that was the reason for the faulty indications was the light switch. After landing; local Maintenance found that incorrect LED bulbs had been installed in these switches causing them to illuminate when the light override was selected.


Second narrative: After swapping aircraft in ZZZ; we pushed back to depart for ZZZ1. Everything seemed normal throughout the aircraft preflight; taxi out; takeoff; and climb to altitude. We reached FL410 heading out over an ocean route. Captain was Pilot Flying on this leg and desired to have the cockpit illuminated to aid us in staying awake and alert during the evening. Captain turned on the LT OVRD switch.A few minutes later our attention was drawn to the overhead switch light panel. We observed that both generator DRIVE switches were illuminated; both bus switch lights had ISLN illuminated (with the switch in the normal switch 'in' position); and the window heat switches were all illuminated INOP (also in the normal switch 'in' position). We pressed the Recall button on the EICAS to see if there were any associated messages; we did not see any.Concerned; that we may have some type of impending generator failure; I was directed to start the APU for system redundancy. At this time; the Captain transferred the radios and controls to me; so that he could better facilitate running QRH checklists and communicating with dispatch and maintenance.We both felt that continuing routing over the ocean was not a good idea. So while he was getting in contact with dispatch over SATCOM; I coordinated with Center to get routing that took us back toward the coastline. Neither the Captain; myself; nor Maintenance Control knew what to make of all of these system lights without associated EICAS messages. The Captain continued to hold on the line waiting to have a chief pilot weigh in on the matter; while also running the QRH.The BUS TIE ISLN checklist is a conditional checklist; in which it only alerts the crew to the meaning of the condition with no further action required by the crew. Captain began to run the generator DRIVE checklist. That checklist directs the crew to open the switch safety cover and mechanically disconnect the drives. We both conferred and felt uncomfortable doing that knowing that was a permanent condition that would leave us with a single APU generator for electrical power.Since the QRH was directing us to take somewhat drastic measures; we felt that a diversion was necessary. Captain agreed with Maintenance Control that ZZZ1 would be the best place to go given aircraft position and their ability to address the situation at that airport. I [advised ATC] and made them aware of our intentions to divert to ZZZ1. They proceeded to give us radar vectors and a descent towards the field.Our duties at that time transferred to preparing and briefing a descent and approach to ZZZ1. Captain got weather; performance numbers; and set the aircraft up for an approach to Runway XL. We were descending out of FL230 for FL210 when we got the descent checklist complete. Captain turned off the LT OVRD light. We immediately noticed that all the switch lights that concerned us extinguished. We cycled the LT OVRD switch several times and realized that there was a direct correlation between that switch and those lights being illuminated.At this point; with the [priority handling requested]; the fuel burned; and the simple truth that there was definitely something wrong with how the overhead panel was wired; we continued with our plan to land at ZZZ1. With approach control; we let them know that we no longer felt the situation [required priority handling]; so we proceeded with normal priority to the airport.Captain and I parked and secured the aircraft. Maintenance personnel came onboard and we proceeded to explain to them all that had transpired. They proceeded to root around in the cockpit trying to ascertain the source of the anomaly and were quite grateful that we didn't mechanically disconnect the drives. After about 45 minutes; they discovered that an LED type bulb (which is the wrong type) was used in those switch lights that have a lower resistance to illumination then the bulb that should be used.Extreme caution needs to be taken that the correct parts; no matter how seemingly minute; are installed in the aircraft. Little light bulbs that do not act appropriately and cause erroneous indications to the crew; could have detrimental effects on a flight.


Synopsis: B767-300 Captain reported incorrect bulbs were installed in cockpit switches; causing lights to illuminate incorrectly and requiring a diversion.