Left and Right brake lights not working, third ok.. UPDATE post #8
 

The bulbs are good, and all the other rear 'tail' lights are working.

Just the left and right brake lights aren't. However their bulbs are good.

I am getting the yellow 'brake light' indicator on the dash when i push the brake the first time after start up.

Fuses are good.

How can I start addressing this problem?

I MUST fix it by this weekend.

Thank you for your help!!

Is this a job for the mechanic then?

No it's really not. Its just really basic electrical troubleshooting. And no one can really walk you through it. Obviously the brake pedal switch is good, so now it comes down to testing continuity of all the wires and the tail light assemblies themselves. If you haven't done any of that, there really isn't enough data here for anyone to respond to.

It could just be the bulb holder is shot. They are pretty basic so if they corrode or crack it could easily cause the lights not to light up.

Do your running lights/turn signals/reverse lights all work?

Jason

Thanks for the replies guys!

Ok so I'll get my multimeter and I'm testing for voltage while the brake pedal is pressed down. I guess I'll start where you screw the bulb in, then go to the harness connection. After that, the wire goes deep into the siding of the car presumably up to the brake pedal switch?
I have tried googling for a brake light diagram but it's hard to find. Anyone have any hints where I can find one?
I need to know what harness pins are for the brake lights so I can see if the power is stopping at the plate or before the plate.

Yes all other lights work properly.
And the bulbs currently screwed into the brake section, work when I put them in the blinker section. So the bulbs are good.

That little nubbin of metal at the bottom of the bulb, looks like it melted and went concave. Maybe I should try grinding away on that base plate and do the electrical testing.

I'm going with Jason on this one, if all other lights work.

Attachment 25511

Thank you! I really appreciate it.

Ok FYI:

On A4 B5 cars, the brake lights share the turn signal lights.

So it is not the adapter or bulbs, because all lights work but L and R brake lights.

Using a multimeter told me nothing useful.


Does anyone have a part number for ATW a4 b5 brake light switch?

Are there 3 circuits? 1 for left, 1 for right, 1 for third brake light?

This seems to be an unsolvable problem but I have to solve it so I can register the car.

Yes, but there are two filiments in those bulbs. On the bottom of the bulb there are two contacts. It is possible that both bulbs are bad, and that the tail light filiment works fine but the brake light filiment is dead.

It should tell you a lot. If you test from the ground to the contacts at the bottom of the brake/tail light bulb, one should have 12 volts when you step on the brake, the other should have 12 volts when you turn on the lights. If you get 12 volts on a contact when you hit the brakes, either the bulb is bad or the bottom of the bulb is not making good contact in the socket.


There is only one brake light switch. Elsewhere in Clayson's drawing, it shows the brake switch connecting to the ECU. Then box 64 in Clayson's drawing is connected to the ECU through the instrument panel wiring harness. Since your high brake light works, the brake switch works.

If you look at Clayson's drawing, the signal from the brake switch comes into both the right and left brake lights, then from the left brake light to the high brake light. If you don't want to track all the down, this drawing tells you it's all one circuit so you could just run wire from the high brake light to both brake lights in the fender.

But first I'd check the sockets with your multimeter to see if there's a signal there.

I just re-read and saw this. Have you tried new bulbs? The fact that you got them to work in the blinker socket doesn't mean much. There are two filiments in there, and if the bottom is messed up the brake filiment may not be getting a signal.

Ok so brake lamps are on the bottom.

So they don't share turn signals.

They share the tail lights (that turn on with the headlights).

I never tried this bulb in any other socket because of two reasons:
1) It was the only double filament setting and I don't put a round peg in a square hole
2) When I was instructed on which bulb to buy, it was a single filament bulb. That must have been a big mistake on autozones part and an even a BIGGER mistake on my part for trusting that crap. I never do, this one time I did and it screwed me.

So the bulb COULD still be the culprit

One of the filaments could be out, while the tail light filament remains good. Right?

Thanks for responding!