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2003 Mustang GT - Brake Light and Signals Issues

5582 Views 7 Replies 3 Participants Last post by  silverandrew
Hello All! Newbie to forum, this is my second mustang.

Got a few issues with my 2003 GT and was wondering if they could all be related (seems to be all lights/electrical) or if one or two is separate.

Brake Lights not working (all 3, left right center)
Backup Lights not Working
Turn Signals not working
Cruise control not working

It has a viper alarm system that was on the car when I purchased it.
Had to fix her up with a new k-bar after a curb incident, cruise control hasn't worked since then.. (airbags went off and they replaced those as well)

I have checked all the fuses;
Checked tail light bulbs; replaced one that was bad.. others are fine or at least look that way...
Pulled all bulbs in the third brake light and inspected them, they look fine. Replaced the one bulb on it that is for the trunk light, and that works fine! Oddly enough while the rest of the lights for the brake don't turn on..

Cruise control not working; I am guessing this is an issue from when they reinstalled the airbags in the steering wheel.

the turn signals started working intermittently about a year ago. They barely ever work now.

Flashers/Hazards work fine! Oddly enough.

Backup Lights just went out same time brake lights went out recently..

Any help would be greatly appreciated!
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The high mounted 3rd brake light not working indicates a basic problem in the circuit. Please perform all tests and report the results.

Confirm power in and out of fuse F2.33.

Confirm there is no power at fuse F2.41 and F2.35 with the brake pedal NOT pressed. Next repeat the test with the brake pedal pressed.

If power at F2.33 and no power at F2.41 with the brake pedal pressed, look at the brake pedal switch (BPS).

Confirm key on power in and out of fuse F2.11 (back up lights).

Check the G400 ground in the truck. There are several black wires that come together under a green screw/bolt.

Check the grounds around the radiator core support. Are they clean and tight?

Finally you may also have a problem with the multi-function switch. However IMO you should rule out a basic brake circuit problem before focusing on the multi-function switch. Again, the high mounted 3rd brake light does NOT pass through the multi-function switch. So the first order of business is to get the 3rd brake light working.
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wmburns :cheers
I will test that out this weekend with my buddy, he has an ohm meter.

will keep you posted
Also check how the alarm is wired up, my boy who is out at Camp Lejeune picked himself up a used C5 that had an aftermarket alarm. Everything had worked fine until he had to replace his battery then it caused all sorts of screwy electrical issues (windows, door locks not working, DIC having issues, alarm going off while driving). I walked him through removal off the alarm and the car worked fine. Depends on how they tied into the ignition (cut off). I have seen a lot of them run to fuse blocks that cause all sorts of headaches.
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I posted the alarm because of that reason! I found the documentation on it, but need to read through it to see if it's just the module documentation, or install as well.

Will keep in mind while testing this weekend. Thanks Sonic
Found the issue!
I tested the fuses, bought a tester at autozone..

I tested the fuses, all lit up to 6v+ but the f2.11.
Had no power to it at all, was wondering and then I happened to look at brake pedal all the way up and the connection there.

I jammed in the connector and had my roommate check the brakes lit all up.
Is this going to require soldering? I think the switch is fine, it's just the wiring out of it. Do I slip the switch off and unscrew the wiring housing? Not a big electrical guy here.
EDit: It's the green wire, its completely burned out of the connection.
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The picture URL isn't working for me. However I'm not sure it matters.

The Brake pedal switch is less than $10. Replace it and then repair the wiring. When something electrical overheats it usually does it for a reason. Not wise to take chances.

Once in my younger days I has a CB radio <I can hear the groans in the back ground>. The power line was fused but the line I tapped got pinched between the metal of the quick removal security bracket and shorted out. It was astonishing just how fast the inside filled up with acrid smoke. Very dramatic sticking head out the window while trying to pull over!

BWD - Brake Light Switch
Part # S646
BWD S646 - Stoplight Switch | O'Reilly Auto Parts
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I just figured it was fried out from the connection touching the plastic housing. My friend soldered the wire back to the connector and the brakes all work, cept the same spot started smoking for a split second when i hit the brakes the next day. Hasn't happened again, but better safe than sorry.
I'll have to pick up a new brake pedal switch at autozone and get the housing from ford, they don't sell that at autozone.

Still have issues with the turn signal and haven't checked cruise control yet. I'm sure those two may just be the switch in the steering column, as the fuses all are good.

Thanks for the heads up, I feel kinda silly that I didn't notice the wire before when I first checked.
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