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Discussion Starter · #1 ·
For some reason my driver side trailer brake light is stuck on.

Has anyone heard of this? If i put on my blinker it doesnt change. I have 12V constant at the plug, is there somewhere it could short? Im going to pull the plug on the truck apart and see if somehow its shorted there, but I wanted to see if anyone has seen this before and maybe it comes from somewhere else?
 

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Quite a few folks have had damage to their wiring harness as it runs inside the frame rails, due to the spare tire not being winched tightly and center, causing fretting of the wires.

Pretty easy to winch down the tire and check visually.

I don't have a 98 manual, so I can't definitively help with the wiring on yours.

section 8W-51 in the free 96 manual (sticky thread at the top of the power train forum) gives details of the operation of the 96-97 circuits, not sure how much they would change to 98. Section 8W-54 covers trailer tow.

So the driver's side stop lamp on the truck is not stuck on, only the trailer light? Is it on any time the trailer is plugged in? any time the headlights are on? any time the engine is running?

Your check of the jack on the truck is a good place to start.
 

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Discussion Starter · #3 ·
Quite a few folks have had damage to their wiring harness as it runs inside the frame rails, due to the spare tire not being winched tightly and center, causing fretting of the wires.

Pretty easy to winch down the tire and check visually.

I don't have a 98 manual, so I can't definitively help with the wiring on yours.

section 8W-51 in the free 96 manual (sticky thread at the top of the power train forum) gives details of the operation of the 96-97 circuits, not sure how much they would change to 98. Section 8W-54 covers trailer tow.

So the driver's side stop lamp on the truck is not stuck on, only the trailer light? Is it on any time the trailer is plugged in? any time the headlights are on? any time the engine is running?

Your check of the jack on the truck is a good place to start.
Truck off, as soon as I plug in the trailer 7 pin the lights come on, its definately a short to 12V+ just didnt know if there was a switch in these that could go bad or what.
 

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I would look for a wire to wire short (through worn out insulation)near your trailer plug. The house load wire sounds as if it is shorted to the right brake light wire. This would be pin 3 to pin 6.

If you pull your trailer tow relay from the Power Distribution Center (PDC) under the hood, and the right light goes out, you would know.
There is a 40 amp fuse in the PDC, fuse 7, that feeds the high amp loads on the trailer (brake controller directly off the fuse, house loads through the trailer tow relay.)

Obviously this info is from a 96 manual, and for a truck with the factory tow package, so it may not be exactly correct for your truck.

Are you sure it is not simply a wiring error? If you really had a wire to wire short, I would normally expect it to reflect back into the truck, causing your truck right brake light to also be on.

Good luck.
 

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You have 12 volts when and where? The brake light wire should not have voltage when no foot on brake. There should be an always hot 12v wire in the 7 wire plug. It may be shorted or corroded in one end of the plug or the other.
 

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Discussion Starter · #6 ·
Ill check it today and see where I have power.

I have one of the 7 pin plugs that tells you what is energized (pretty cool plug) and its saying I have 12V on the left brake lights.

I also noticed last night if I put on my 4 ways the trailer lights stay solid.

I think the plug on the truck might be bad, but I agree if I had power to the trailer lights I should have a brake light on the truck on.
 

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Check for corrosion in the truck plug and check the flashers.
 
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