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Both of my brake lights were not working. I found the switch by the brake pedal was broken. Just replaced that, but now I see that only the passenger brake light comes on when I press the pedal. Of course I thought it was just a bulb issue, but the bulb looks fine and I even swapped it and when I put the driver's side bulb in the passenger side socket, it works fine. So, it appears to either be some sort of wiring problem, or perhaps that socket? Does anyone have any suggestions, or ways to test the system? I have not done anything electrical on this car at all and don't really know where to start.
Let's start with: Do you have a wiring diagram and a multimeter, and know how to use them?
IIRC, your car has external grounds at the sockets/lens assemblies. Are they all intact? Swapping the bulb over was good. Perhaps you can check the ground with an alligator clip lead.
I do have a meter and know how to use it! I have the AIM as well, have to locate that and see if there are electrical schematics in it... I think there are? I also see you posted aink to done as well... Thanks!
Basic stuff. Do you have power to that socket when the brakes applied. Yes, check grounds. No, start backing up. do you have power coming out of the turn signal switch? Check at the steering column connector, No? Bad contact in signal switch. Yes, keep following the wire to the back of the car. Power under the door sill? Yes? Keep going or splice and run a new wire. No? Splice at steering column connector and splice into wiring under door sill. Basic stuff.
If you have brake light power coming out of the turn signal switch (you already know you have power going in as one side works) And you don't have power at the rear of the car it is often times quicker and easier to just run a new wire than try to find the break. if you have power, then obviously a bad ground.
2025 c3 ('74-'82) of the Year Finalist - Unmodified
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First test the socket by attaching a wire to a good ground and touch the other end of the wire to the brass part of the socket, if the bulb lights up the socket is bad.
Next see if you have power at the yellow wire coming out of the harmonic connection (at 'M').
If you have power at the harmonica connection, but not at the rear socket look at the 12 pin connector near the left kick panel/
What everybody said ^^^^^^^and. I fixed my rear lights when I found a splice in the wire going to one of the rear sockets. The splice LOOKED good but after I unhooked it, cleaned it up, then reconnected it, the rear light started working. There had to be corrosion on the twisted wires.
First test the socket by attaching a wire to a good ground and touch the other end of the wire to the brass part of the socket, if the bulb lights up the socket is bad.
Next see if you have power at the yellow wire coming out of the harmonic connection (at 'M').
If you have power at the harmonica connection, but not at the rear socket look at the 12 pin connector near the left kick panel/
Thank you so much for this....stupid question - but how do I get that socket removed?
Thank you so much for this....stupid question - but how do I get that socket removed?
I'm not sure your car has that type of socket. But of you can get to the bulb to change it, you can remove the bulb and do this experiment. The two pins at the bottom are for taillights and brake/indicator, and the shell should show continuity with ground (negative battery terminal, and most black wires in the car).
One brake light not working
