Modded Mustang Forums banner

1 - 6 of 6 Posts

·
Registered
Joined
·
930 Posts
Discussion Starter #1
I installed a carbon fiber trunk lid not so long ago. I noticed that the third brake light along with the trunk light stoped working. I got some new bulbs and still had nothing. So I used a multi meter and tested power right at the bulb sockets, I have power and good grounds, but still no light or third brake light. We are at a lose with this one. I didnt check the 10a fuse cause my other brake lights are working fine. We also thought that maybe the trunk lock unit used the steel trunk lid as a ground, but my trunk lock is working which means the harness is getting power and a good ground. This is very frustrating. One thing I did find weird is that the harness uses a constant power, Im sure its normal but I found it weird. Any help would be sweet.
 

·
Registered
Joined
·
13,628 Posts
Try holding a wire against the light housing mounting points/bolts, or maybe the housing itself, and ground the other end and see if that works. I got a feeling that the non-conductive carbon fiber is the culprit.

And the trunk release wiring is a constant so you can pop your trunk whenever. I don't think that circuit is going to share a ground with your lights.

Scanning over the electrical schmatics shows the ground for the luggage light and high mount brake light are dedicated and do not return through the harness, so this might fix your situation. Or tap the black wire coming out of each fixture and run that to a ground and see if that works.
 

·
Registered
Joined
·
930 Posts
Discussion Starter #3
We did try runing a ground from the mounting bolts but no luck. Now that you say they share the same ground Im going to try that. I lost my schamatic book over the winter which doesnt help much lol.
Thanks again 07 Boss.
 

·
Registered
Joined
·
13,628 Posts
We did try runing a ground from the mounting bolts but no luck. Now that you say they share the same ground Im going to try that. I lost my schamatic book over the winter which doesnt help much lol.
Thanks again 07 Boss.
Well there not the same ground, but they definitely don't look like they return through the harness. Look for a black ground wire coming off each fixture and tap that to a ground and see what happens.
 

·
Registered
Joined
·
930 Posts
Discussion Starter #5
Just checked and all grounds leed back to main ground on harness, so since my trunk release works it leeds me to belive that all grounds are good. I took the harness apart to confirm it. I am ready to burn it down lol. It just makes no sence.
 

·
Registered
Joined
·
930 Posts
Discussion Starter #6
Ok just got trunk light to work, it was a sticky trunk spring. But the upper brake light still no go. Still got a good power and ground right at the bulb socket, yet no light. I put it in my friends car and it worked fine.
 
1 - 6 of 6 Posts
Top