Brake light wiring short

[prac345]

I am a recent owner of a 2006 xc70 which is in great shape for its age. Recently the left brake light out went out, and it is reported on the dash. I assumed that the bulb had burned out, but upon pulling out the housing for the bulb, I noticed that one of contacts looked blackened as if from a short. I went ahead and replaced the bulb and cleaned the contact with steel wool and replaced it anyway. To no surprise it didn't work. I tried swapping the bulb housing and bulb to the right side to see if the problem moved. No, it stayed on the left side, so it is not the housing.

So it seems to me that it must be a wiring problem, specifically for the left side, since the right side continues to work.

How do I approach solving this problem? From the user manual, it shows the brake fuse as being just below the steering wheel. I haven't opened that up yet, but can someone tell me where the brake circuit splits into left and right branches on its journey to the rear lights. Do those wires run underneath the car?

As you can gather, I am in the enthusiastic but ignorant category, and I hope that someone can point me in the right direction.

Thanks

[Georgeandkira]

I cannot answer you question about the routing of the wiring but I can tell you what I learned when my rear brake light went out.

As in your case I had the blackened contact on the bulb's holder. The metal in the holder is curved as you likely recall. I assume this facilitates smooth contact as the holder is twisted into place. The point where the holder contacts the fixture is flat metal and was equally scorched. Did you clean it too?

I'd make sure the receiving element of this inexcusably flimsy circuit was cleaned and had a thin coating of dielectric grease before tearing into the wiring.

One smart and efficient thing you can do is use a volt meter or test light to see if the metal in the fixture is energized when a helper applies the brake.

Keep in mind that any former owner or stooge he hired to install bulbs could EASILY have jammed the damn bulb holder (aka socket) into place and bent the metal in the fixture.

Was your plastic holder at all scorched or melted? I had to shave mine flat because it had warped a bit. Such warpage or bubbling of plastic can EASILY keep one or the other or both contacts from being made.

Again (because I'm a pedantic know-it-all) be certain your cheap plastic parts are allowing the metal to make contact.

Another thing I recommend doing is apply a brick to your brake pedal when doing this work to keep the circuit energized. I found that wiggling the holder in place got my lamp to light. The amount of plastic I needed to shave away was not insignificant.

I hope some of this helps. G&K

[prac345]

Thanks for taking the time to reply!
I didn't actually try to clean the contacts on the receiving element. That's a great point. I had trouble getting my hand in there to get the bulb inserted, but I will give that a try. It looks the plastic housing is melted in part, although I don't think it got hot enough to deform in my case. Also, I hadn't thought about a dielectric grease either.

Thanks for all the advice and I will give it try.