Brake Light Problem

[911TurboLook]

I am currently having a problem trying to locate a short that keeps blowing a fuse. The fuse is for the brake lights.

I have done the following to try to isolate the short:
1) Disconnected the rear lights (unplugged from the connector)
Right disconnected- result: blown fuse
Left disconnected- result: blown fuse
Both disconnected- result: blown fuse

2) Disconnected one brake light switch- result: blown fuse.

3) Disconnected the other brake light switch- result: fuse NOT blown.

4) Reconnected the first brake light switch (number two above) result: blown fuse.

My drawing shows that the only connection made to the brake light wire (after the switch) is one that goes to the cruise control. I do not know where the connection is made. The cruise control module is removed. The short is between the brake light switch and the rear lights.

Does anyone have suggestions to where a short could be?

- Thanks

[redstrosekNic]

Are your brake/ blinker/ back up lights on the same fuse? I had a similar problem, and the back-up light harness melted because of the muffler.

[911TurboLook]

Originally Posted by redstrosekNic

Are your brake/ blinker/ back up lights on the same fuse? I had a similar problem, and the back-up light harness melted because of the muffler.

Hello-

Blinkers/Back Up lights/Fog Lights/Headlights/Emergency Lights are all working and are on a different fuse.

The only wires on this fuse are for the brake lights and cruise control.

- Thanks

[DRACO A5OG]

What have you done to the car prior to this issue?

It may sound simple but are you certain the bulbs are placed in the correct position? Even though they have staggered notches, if you press hard enough it will still go in wrong.

Check the ground too, it sit in a very harsh environment behind the light housing.

[911TurboLook]

Originally Posted by DRACO A5OG

What have you done to the car prior to this issue?

It may sound simple but are you certain the bulbs are placed in the correct position? Even though they have staggered notches, if you press hard enough it will still go in wrong.

Check the ground too, it sit in a very harsh environment behind the light housing.

Rebuilt the transmission, New flywheel, New clutch, resealed engine, a restoration of the exterior (All new trim, front spolier, lens, etc.). I am currently doing the interior and have found that the brake lights do not work.

The taillights have nothing to do with the problem. I have isolated the wires (unplugged them) from the brake lights and the fuse still blows. The light housings have all been gone through (cleaned/etc) and worked.

Thanks,

Jason

[DRACO A5OG]

Where in Cali are you? If SoCal I can stop by and take a peak

[911TurboLook]

Originally Posted by DRACO A5OG

Where in Cali are you? If SoCal I can stop by and take a peak

North Cali, North of Yosemite. About 7 hours away from San Pedro.

[DRACO A5OG]

Hah, I can get there in 5 LOL

Sorry can't help further Brother!

[DRACO A5OG]

Hah, I can get there in 5 LOL

Sorry can't help further Brother!

[ossiblue]

I'd bet on a problem with the former cruise control connection, as you suspected. Never having had one on a car, I cannot direct you where to look but I'm sure someone will offer up help soon. From looking at pictures on the forum, I believe it was on the left side of the engine some where.

[911TurboLook]

May have solved the problem... I will let everyone know if I have.

[911TurboLook]

Fixed my brake light problem, maybe/not. With the help from Geary (86 911 Targa) I was able to isolate the brake light circuit by removing both wires from fuse #7(from the left). After unplugging both brake light switches I checked each switch terminal to ground. I did not find a shorted terminal. After placing one test probe in the brake light socket I verified the wire between the switches and the fuse block. I then removed the wire from the fuse block and checked that it was not grounded. Removed the cruse control controller located under the dash. All measurements from this point were measured between the brake switch leads and ground:

1. The first measurement was less than 0.5 ohms, which was expected because each lamp measured about 0.5 ohms. (Three lamps in parallel.)

2. Disconnected the rear lamps by unplugging each rear light fixture.

3. The third lamp in the center of the back window was removed.

4. At this point I had a resistance measurement of 25 ohms. This would place about a 2 amp. additional load on the fuse, so that could be the problem.

5. At this point, I could not think of anything to unplug. This is where it gets strange. Standing around, I was looking at the relays in the trunk and just for the fun of it, I unplugged and then plugged them back in. I looked at the DMV and it was measuring infinity! I can’t explain this; the relays had nothing to do with the circuit I was trouble shooting. I gave up for the night.

6. The next day, the measurement was still infinity. I connected the wire to the brake light switches, plugged all lamps in and replaced the 8 amps. fuse. Every lamp lighted when the brake was applied and the fuse did not blow. Been working since.

- Jason

[3Pgarage]

Jason, did your troubleshooting spree finally result in unplugging the cruise control module?
My issue is the alternator light comes on when the brake pedal is pressed. No fuses get blown.
Did you ever find the tail-light ground in the wheel well?
Thanks, Frank