Electrical Brake light abs turn signal issue

Tristanornce

New Member
Dec 29, 2021
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Lees summit missouri
Hello, after months of this issue I thought I’d get other peoples opinions because I am stumped. On my 05 mustang gt, the brake lights and turn signals do not work. When I turn my night time running lights on my brake lights do turn on but when I press on the brake pedal they do not illuminate. (My head lights and front turn signals work fine). My turn signals in the rear do not work, but my trunk lid third brake light does work. When I do use my turn signals they will blink fast indicating that I have something wrong, and my hazards also do not work. I have replaced the wiring harness, bulbs, and checked the fuse in the smart junction box. If anyone has any idea on how I could fix this without spending thousands at a shop I’ll send cash your way!

Thank you!
 
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7991LXnSHO

wanna catch the space herp
10 Year Member
Sep 1, 2010
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Kearney, NE
No cash needed if I can help.
On older cars where the bulb holding socket grounds to the lens housing, the answers would be to first check the grounds and run a separate ground wire from the socket to ground. It still would be a good idea to see is the ground wire is making a good ground connection. (Do you have a multimeter?)

Without looking up part numbers, I’m still sure you have dual filament bulbs in the taillights. One filament in each bulb comes on for night time driving, and the other filament lights for the brake pedal and flashes for the turn signal. Pull the socket and see if both filaments are working right.

So, if the turn signals on the dash and up front are working, but the rear ones do not and they flash fast, it’s time to test or replace the rear bulbs and make sure the rest flash. The blinker’s load being off usually makes the fast blinking for a bad bulb. (You might/probably have a lighting module instead of the separate TS and hazard blinker cans by 2005. At least my G. Marquis does. It was recalled, and I have not messed with it or even tried to find it, but it also included headlight relays.)
So, if I did not make sense, please ask questions. If I did, please let us know what you find. Hopefully it’s something simple, and not a darn rodent chewing issue.
 

caliber92

Active Member
Mar 30, 2015
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No cash needed if I can help.
On older cars where the bulb holding socket grounds to the lens housing, the answers would be to first check the grounds and run a separate ground wire from the socket to ground. It still would be a good idea to see is the ground wire is making a good ground connection. (Do you have a multimeter?)

Without looking up part numbers, I’m still sure you have dual filament bulbs in the taillights. One filament in each bulb comes on for night time driving, and the other filament lights for the brake pedal and flashes for the turn signal. Pull the socket and see if both filaments are working right.

So, if the turn signals on the dash and up front are working, but the rear ones do not and they flash fast, it’s time to test or replace the rear bulbs and make sure the rest flash. The blinker’s load being off usually makes the fast blinking for a bad bulb. (You might/probably have a lighting module instead of the separate TS and hazard blinker cans by 2005. At least my G. Marquis does. It was recalled, and I have not messed with it or even tried to find it, but it also included headlight relays.)
So, if I did not make sense, please ask questions. If I did, please let us know what you find. Hopefully it’s something simple, and not a darn rodent chewing issue.
We will try this troubleshooting when we start working on my friend's '06 GT project. The brake lights are malfunctioning intermittently. The car is still in the shop for the installation of the brake pads and new set of tires from 4Wheelonline plus the alignment.