GD993C4

Your help would be appreciated to troubleshoot a problem that I am having with my third brake light. Today, I realized that my third brake light was not functioning. So I followed the instructions on p-car.com (great site) to remove and inspect the 3rd brake lamp assembly and circuit board. What I found was four burnt lamps. However, none of the lamps illuminate when I brake. I have 11.7 volts at the leads that connect to the lamp circuit board assemble. However, no voltage at the circuit board. What is strange is that if I rig a 9 volt battery to either the circuit board or leads going to the circuit all of the working lamps (approximately 18) illuminate? I did a visual check of the board to look for a short and couldn't find one. Any help on additional troubleshooting tests/check or explanation on why 9 volts from a battery works and 12 volts from the car doesn't would appreciated. Thank you.

993James993

Do you have a cab or a coupe?

mr_bock

Not sure why the 9 v works and the car 12 v doesn't. I dumped the OEM bulbs and put in LEDs. There are some very good DIY write ups on this. LEDs last way longer than the bulbs.

Good Luck!!!!

GD993C4

It is a coupe.

FlatSix911

Here is a cheap replacement listed on Ebay ....

http://cgi.ebay.com/ebaymotors/Porsc...spagenameZWDVW

GD993C4

Thanks, however I am not convinced that I have a faulty 3rd brake light. I am concerned that maybe I have a wiring issue where I obtain 12 volts but without enough amps to drive the lamps.

993James993

Check to make sure you are getting voltage at the contacts on the top of the rear window, inside the car. Your problem could be a cold solder joint there.

Some have used liquid solder to repair this. Do a search in this forum. (If you can't find it PM me and I will try to locate the thread for you.)

You can also try this alternative method, courtesy of Gert Carnewal: http://p-car.com/diy/glass/ (You may have to visit http://p-car.com/diy/ to gain access to that page.)

GD993C4

I am measuring approximately 12 volts inside the car on the contacts by the rear window.

993James993

Are you getting 12 volts outside the window? The break could be on that side.

GD993C4

Yes, I get 12 volts right up to the two contacts on the 3rd brake light circuit board (that has all of the lamps on it). However the light do not lite-up. They do however 'lite up" if I attach a 9 volt battery to the same terminals. My electrical ability is limited to using a digital volt meter and hope that someone has had a similar problem

993James993

Gary, so you have 12 volts to the light at the circuit board, and it doesn't light when you depress the brake pedal. Do the other brake lights come on?

At this point it sound like the issue is not the light but how it is activated.

GD993C4

The other brake lights work. I just bought some wire clamps and will try to connect the 3rd lamp from the leads inside the rear window to confirm that the power and amps are OK from that point. Any other suggestions would be appreciated.

GD993C4

It turned out to be the ground wire (brown wire) going throught the rear window. I followed the repair procedure and it is now fixed.

993James993

Excellent! Good for you.

Gert

The typical conductor failure.
Good to hear that you got it solved .