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I have the 72 service manual it is different were grounds are on the frame. I have one taillight socket i replaced and after splicing together all three leads i have a Dimmig brake lite comparing to the driver's side is bright. prior no brake lite at all now a dim brake lite
I see a splice point near the license plate. It shows a tap for each side marker tail and back up. This is shown on one of my C3 books which i have them all. The frame point on drivers side has a couple of taps which one goes to the main tap. I must have a bad ground for the tail lamp is not as bright as the drivers side. The race way that all the wiring is in is barely accessible because of the black corrugated wrapping. I do not want to pull the rear bumper because of the 100 attaching points which i had to do when i shot the rear bumper off the car. Any suggestions would be appreciated.
I have a 77 car. The question specifically stated 77.
so I answered, I also have the 77 electrical trouble shooting manual. And all the Genuine GM service manuals.
so, sorry I answered.
But in both, it looks like there is a black wire that attaches to the port side rear chassis.
Yes, early & late harnesses are different but the ground point is the same.
The antenna mount ground strap to frame is the same where rear harness ground wire eyelet attaches...
If you're fuel gauge and other lamps are working properly then you are getting a good ground at the rear harness ground wire eyelet. You have to peel open the split conduit to find the fault...
This is a Late or 2nd design rear harness...
The splice joint for the ground(s) and Brown wires for Park/Stop/Turn/License & Side Marker lamps is 31" from the ground eyelet into the split conduit...
I had a ground wire fail inside the bulb socket. I think 75-82 all use the same part.
What is the specific issue you are trying to troubleshoot? Have you tested for continuity? The ground wire should have continuity to the inner shell of all four taillight sockets.
Originally Posted by Bikespace
I replaced the rear bulbs with LEDs within weeks of buying both cars. For reference, the outer sockets (brake/turn) take 2-circuit 1157 bulbs. The inner sockets (reverse lights) take 1156. In my 80, gremlins prevented my upgrade from working. No surprise, my car had sat for a while. What was a surprise was the source of the problem. One of the sockets had an internal connector fail, causing an intermittent ground failure in the circuit.
The solution, of course, was to replace all of the rear sockets. I used 3-wire, 2-circuit 1157 sockets in all four positions, and swapped the inner lens assemblies for all-red lens. The stock lenses are keyed, so I drilled a second hole in all locations, making it possible to swap to four red/white lenses if I ever want to.
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Originally Posted by Bikespace
I had a ground wire fail inside the bulb socket. I think 75-82 all use the same part.
What is the specific issue you are trying to troubleshoot? Have you tested for continuity? The ground wire should have continuity to the inner shell of all four taillight sockets.
Attach a wire to a good ground and touch the other end to the brass part of the bulb holder, if the bulb lights you need a new socket.
Okay thanks for all of your help! The problem was the single brown wire was not making contact all the time. It was giving me a dimming brake lite and no parking what so ever. After adding the new 3 wire socket and spiceing with crimp butt connectors and a new 1157 Sylvania lamp every thing is okay now.
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