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Hello all, recently acquired a 1978 C3. It was very poorly wired, and tons of stuff had been spliced in over the years. Got it mostly back to stock taking lots of sketchy stuff out. I went to check functions of tail lamps and have a few problems. FACTS: 1. Brake lights work but are very dim. 2. When headlights are switched on the taillights and side markers work as they should, but the brake lights no longer function at all. 3. Turn signals function fine regardless of the situation.
This is all with the car not running. I saw a few thread where someone mentioned the ground for the whole rear lamp harness. I tested the resistance and determined the ground is good but just for good measure ran a lead directly from the battery to the rear lamp harness ground. Same thing happening. Dim brake lights and no brake lights when headlights are ON. I am stumped have done full wiring harnesses on many other vehicles and never ran into anything like this.
2025 c3 ('74-'82) of the Year Finalist - Unmodified
2019 C3 of Year Finalist (appearance mods)
Hi and Welcome.
Check that the bulbs are 1157 and installed correctly then run a wire to a good ground and touch the other end of the wire to the brass part of the bulb holder.
If everything works correctly then replace the socket.
Thank you Peterbuilt and Hazmatr. Tried both of these suggestions with nothing changing. I did however replace the weird led bulbs that were in all the lights with new 1156's and 1157's. Now I have no brake lights at all. I pulled the plug off the brake light switch to check the voltage of the orange and white wire. If I'm correct the orange wire should be 12v and when the brake is pressed it should feed the voltage through the white wire and into the steering column wiring. Weird part is when checking the orange wire alone it gives me 12v when jumping the white and orange together, to bypass brake switch it reads 0. I don't believe this system works like the ground system of most horns, where the grounding out actually makes it function. What am I missing?
P.S. that manual is fantastic thank you very much!
1978 C3 Rear Taillamp/Brakelight Problems
