Time sensitive brake light help plz
 

Hello,

My daily driver went down for the count yesterday and I need to get my 85 911 ready for inspection asap.

The problem is the rear driver's side brake light. Earlier today, neither the tail light filament nor the brake light was lighting up. I noticed that the #5 fuse was blown and replaced it. Now, the tail light works when I turn on the lights. However, when I hit the brakes, the tail light cuts off and the brake light filament does not light up. THe center and passenger side lights work perfectly.

Any help would be appreciated. I am not mechanically inclined but can rotate a screwdriver if needed. ;-)

P.S. I was told the front passenger side bearing needs to be packed, does that mean I should just ask my mechanic to replace the bearing?

How bright is the tail light when you turn the lights on? Brighter than the other side? If so, you have the wrong bulb or installed incorrectly. If not, then it is some other problem.

Sounds like a short, rather than the more usual ground problem. Use a multimeter.

(Probably get better results stating a new thread with an appropriate subject for different questions)

Probably not, although the bearing might be toast, it probably is simply overdue for routine maintenance - which is to disassemble the bearing, clean/inspect, pack with fresh high-pressure grease and re-adjust so the play is correct (can just rotate the washer under the nut with a screwdriver).

Do both sides - the other side probably needs it too...

That bulb has no ground return connection, low power/current tail light filament is getting its ground return THROUGH the brake light filament(s).

Firstly, the bulbs seem to be equally bright with just the taillights on.

"Sounds like a short, rather than the more usual ground problem. Use a multimeter."

"That bulb has no ground return connection, low power/current tail light filament is getting its ground return THROUGH the brake light filament(s). "

Ok, so let me make sure I understand. What I am understanidng from this is that the bulb has no ground so the ground can't be the problem? That means that it must be a short? If that is right, how do I go about diagnosing a short?

No, the resistance of the brake filament is a LOT lower than the tail filament. Apply 12 volts to the tail filament with no ground for THAT bulb base and the current flow path will be through the low resistance stop filament and then through the other PARALLEL stop filaments and thus to THEIR ground.

If you look closely the tail light with the "failing" stop light will be slightly dimmer.

The Porsche tail/stop light sockets are bad about this.