mse

I have a 2003 C2 coupe with about 60,000 on it and having an issue with the driver's side tail light.

I initially noticed that the brake light was out when my wife was driving the car. Thought...bad bulb, I'll replace it and we'll be good. Replaced the bulb...no joy. Thought it might be the new bulb, but replaced another new bulb and that doesn't work either.

Checked the other lights - fog, turn signal, side marker, etc. All work on both sides...except the brake light on the driver's side. Thought, okay...somehow I've either bought the wrong bulbs or both are defective. Pulled the passenger side rear light assembly and traded bulbs as I know the passenger side brake light works. The new bulbs work in the passenger side assembly and the working bulb from the passenger side does not work in the driver's side. Took a look at the fuses and A4 was blown. Replaced that and figured I solved my problem...nope! I pulled the assembly again to check the connections and all seem to be intact. No loose connections or broken wires that I can see,

I'm at a bit of a loss about how best to move forward from here. It seems odd that the brake light used to work, and all the other lights in the assembly work...except the brake light. I'm generally pretty handy and with the proper instructions can take on most tasks, but when it comes to electrics, I have no idea. The only thing that makes sense is that for some reason, power is not getting to that socket...and just that socket.

I see that the harness for the tail light assembly is $160 depending on where i look for it, but before I go that route and throw money at parts that may well work just fine, I wanted to see if anyone else has had a similar issue. Hopefully there is something simple that I haven't thought of...

Thank in advance for your help on this

gbarron

I'm not 100% familiar with the wiring for your car, but in the situation you described either voltage is absent or the ground circuit is open. With a multimeter (and a helper to step on the brake pedal) you can test for voltage at the bulb socket, then check for continuity to ground. Once you determine which one is causing the problem you should be able to trace it to the source by following the defective circuit and checking for continuity at each connection point. It's possible there is a break in a wire somewhere or corrosion causing a poor ground connection.

TexSquirrel

Great advice.
Multimeter testing is going to be required.
You can also use a PowerProbe or a test lamp to test grounding.(brown wires)

TexSquirrel

This might help you.

De Jeeper

The light socket has failed in other cars. As said above u need a multimeter.

mse

Thanks guys! I appreciate the advice on this. Good excuse to pick up a multimeter - I expect I'll need one again at some point - and figure out how to use it! As I said, I know zero about how the electrics work, but I'm sure there are good tutorials out there to put me on the right path. If you have any suggestions, I'm all ears!

De Jeeper

Real easy on a car. U r looking for 12v so on a bulb socket the center is the + and the outer shell is the -. Or a more modern bulb one side is + and the other is -. If u dont get 12v u then need to test the ground for continuity to a know ground point and the same with the +. Also a prob tester is real easy to use for checking 12v.

Mike Mullins

look for corrosion of contact , even on bulb holders in housings. Multimeter is nice, 12V trouble lite cheap for troubleshooting

playswithcars

It is a common issue for some of the bulb sockets to go bad. I have some good working spare taillight harnesses if you want to replace it.
I'll only charge $40 shipped. Let me know is you're interested!

mse

Thanks for the help guys.!

No issues with corrosion. I checked that before I started going down the path with the fuses. I've picked up a multimeter, so will check the socket in question and one I know works to make sure I'm getting a correct reading.

@playswithcars - thanks for the offer on the harness. If the socket is actually bad, I will likely take you up on your offer. Will DM either way.

mse

Bringing this one back to life because clearly something else is going on here…

I used a multimeter to see if any power was getting to the socket. No power, so either the socket is bad or there is a fuse issue. I checked all the fuses that could be remotely related to the tail light based on the diagram in the fuse box panel. All looked good. Based on the wiring diagram TexSquirrel provided, it looks like the most likely culprits would be either A4 or B7. Both looked fine. I figured the harness must be the issue and picked a new one. Figured that way I know it’s good. Arrived yesterday and installed the new harness today. No joy…the brake light still does not work.

I figure it has to be a fuse issue, but am at a loss as to which one it is. Before I go through and check all the fuses, I thought I would see if anyone has any bright ideas. As far as I know, there is only one fuse panel in a 2003 c2 coupe. I’d hate to think I’ve been chasing a solution in the wrong spot.

Any additional insight would be much appreciated. Thanks in advance for your help on this one.

De Jeeper

It could be the harness between the fuse and the tail light plug. Mice like to get behind the coolant resi and eat the wires.

mse

Thanks for the suggestion. Hopefully there will be an immediately obvious break in the wiring that can be quickly addressed. Good thing we have a long weekend!