Brake Light Switch possible culprit - Diesel Forum

ihochad · 10-28-2009, 04:56 PM

Folks, need some help here. I have a 96 F350 bought from a member here. Been an AWESOME truck and I love the thing, however over the last week I have had some issues with the brake lights.

First, nothing has been added or changed since this problem has started, I searched on ABS light flashing and only found results for blown fuses.

My ABS light is flashing and fuse is blown, however when I put a new fuse in as soon as I touch the brakes it blows. Instantly. This tells me obviously direct ground. However as stated nothing has changed and I have visually inspected the wiring and can find no issues.

Could this be a bad brake light switch causing this??? It doesn't make sence to me that it would be but honestly I am a little out of my leauge here. Thanks in advance for the help!!

speeddemon31176 · 10-28-2009, 08:49 PM

Do your brake lights on your truck stop working then also? If so then I would say that the switch may be grounding itself out some how or you have a short in the wiring somewhere.

**pjwoolw** · 10-28-2009, 10:43 PM

Check the third brake light. Also the trailer wiring.

ihochad · 10-29-2009, 11:04 AM

I checked it all again last night, put a new brake light switch in. Nothing the same deal touch brakes POP fuse blows. And when I say it blows it BLOWS not even a second of hesitation. I am starting to get really frustrated, may actually have to take this to a shop. Any other ideas? Auto parts monkey said maybe the ABS sensor???? That seems unlikely though.

Window&Door · 10-30-2009, 12:18 AM

Same happened here back in February, turned out to be my trailer wiring for fifth wheel.

speeddemon31176 · 10-30-2009, 12:26 AM

Very possible. Try and unplug it from the harness in the back at the frame rail and try again. If that is it the you only have to replace the 7 pin plug assembly.

ihochad · 10-30-2009, 10:58 AM

OK, so last night I thought I would replace the ABS sensor in the dif, no luck still immediately pops the fuse. I had already pretty much eliminated the trailer wiring, but thought what the hell and completely unplugged it. Still, POP the second you touch the brake pedal. The down side is I am moving this weekend and REALLY need the truck. Its bad enought not having brake lights but not trailer brake is not an option with the crap I have to move. Really getting frustrated at this point!

bh96powerstroke · 10-30-2009, 01:17 PM

Ive had that problem after towing a trailer for a friend. Not only did it blow the fuse but it also took out the relay for the blinkers.

Window&Door · 10-30-2009, 06:54 PM

Does the truck have a brake controller?

speeddemon31176 · 11-01-2009, 03:27 AM

Window&door has a good idea there with a possible bad brake controller. I would also climb under the dash and see if you have chaffed wires that could be shorting out the brake circuit.

ihochad · 11-17-2009, 02:11 PM

OK I am getting to a point of simply throwing a match at this thing.

I have done the following with absolutely no change

Taken the entire dash apart to look for a spot that the wire could be grounding.
Unplugged the turn signal switch (to eliminate the hazards) no change. I plugged the turn signal back in and tested the hazards with a new fuse and they work fine with no issue. Touch the brake and bam fuse pops.
Traced all the wires as well as possible and can find no short at all or even slightly worn or fraying of any wire.
Unplugged the battery to reset the computer, no change
I am litterally out of ideas and paitence with this thing. Any help would be VERY much appreciated,
also to the question about the brake controller. Yes I have one but unplugged it and still it blows the fuse. I really need the truck and at this point to don't like driving it without brake lights and certianly don't want to tow without the brake controller.
Also am noticing the brakes feel different, it may be in my head but I really feel like they are different.

WorkinMan · 11-17-2009, 03:34 PM

I don't know if this info will help you at all, but I'll try. I had my brake light switch go out on me last Spring while pulling a small trailer and it WOULD NOT blow the fuse. I didn't have any brake lights, and my truck wouldn't come out of PARK, but it would not blow the fuse at all. And a few years ago, I had the same problem you're having now and I traced mine back to a wire shorting out against the body back by the brake lights. Like you said, DEAD SHORT. Fixed the wire and I've never had any more problems with it. If I were you, I'd spend my time looking for a short in the wiring back around the tail lights themselves, or maybe a short up by the third brake light.
Hope you find it.
Chris

ihochad · 03-16-2010, 05:00 PM

Hey Folks,

Just an update for anyone searching in the future. I finally resolved this issue last week. It turned out to be a intermittent short in the wiring harness between the brake light switch and the 3rd brake light. Rewired that and solved my issues.