tail light goes out when brakes are applied (1 Viewer)

Joined
Mar 30, 2017
Messages
22
Location
Alameda, ca

My passenger side tail light goes out when the brakes are applied. When I let up on the brakes the light turns on to the normal low level. I changed the bulb and there was no difference. I then cleaned the metal contacts on the bulb and the fixture that it attaches to. This worked initially one time, but with further testing it stopped working. Both filaments in the old bulb and new bulb are intact, and the bulb worked at least once, so I don't think the problem is with the bulb. Thus, I suspect there must be a loose connection somewhere. Has anyone else had or solved a similar problem?​

 
Joined
Dec 12, 2021
Messages
18
Location
Blue Mountains, Sydney
Place the bulb in the socket and have someone hold the brake pedal down. Move the socket around and see if there are any sudden changes. Sounds like wires touching somewhere in the harness, was common when I played with old VW's.
 
Joined
Mar 30, 2017
Messages
22
Location
Alameda, ca
Place the bulb in the socket and have someone hold the brake pedal down. Move the socket around and see if there are any sudden changes. Sounds like wires touching somewhere in the harness, was common when I played with old VW's.
I'll give it a shot! Thanks
 
Joined
Apr 14, 2016
Messages
2,282
Location
Oregon
The #1 suspect for weird taillight behavior is the trailer wiring harness. It's behind the right, rear quarter panel trim. Just fish it out -- it's a small box -- and remove it from the circuit.

Edit: to be a bit more clear, pull the large plastic trim piece off, then stick your hand in and feel for the wires coming from the taillight. Then just work your way back maybe six inches and you should find the trailer harness adapter, if you have one.
 
Last edited:
Joined
Dec 10, 2007
Messages
9,003
Edit: he beat me to it.

Does your 80 have the original port or dealer installed trailer harness (US Models seemed to all get this). The connector dangling off the tow bar is known to corrode internally causing odd electrical gremlins.

Check all your grounds particularly in the rear of the vehicle.

Try a new set of bulbs. I once got odd things happening when I replaced a brake bulb, then replaced the new bulb with the other new bulb from the same package, same odd behavior (cruise control going off when I turned on the headlamps). Problem went away when I bought a different brand of tail lamp bulb (neither were LEDs).

Maybe @jonheld will chime in.
 
Last edited:
Joined
Apr 14, 2016
Messages
2,282
Location
Oregon
The #2 suspect is probably the taillight harness. I doubt that's your problem, since you're seeing behavior change when another circuit gets power. More common failures on the taillight harness are the ground wire coming loose from the socket or the contacts getting hammered flat with age.

It's #4 in this diagram:

 

Users who are viewing this thread

Top Bottom