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Brake lights on, all the time.


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I have a 2015 Sierra 2500HD, 4x4, 6.6L Diesel, Crew Cab SLT.

 

I have been rebuilding the front portion of the bodywork due to collision damage. I have it pretty much back together, but it has a couple of electrical quirks that I cannot seem to diagnose.

I would appreciate any help y'all can provide.

 

 

First of all, anytime the battery(s) are connected, the brake lights stay on. All of them. Two bulbs on each side, and the high-third light.

Even when the key is out, the doors are closed, and the truck is locked/armed.

This does not have any effect on headlights. I can turn those on/off normally. When I turn on running lights, the small marker lights on the side of the taillight housing come on as they are supposed to, and the 2 main bulbs go brighter (or the second filament turns on), as they are supposed to.

 

This seems like a pretty simple relay issue, or a wire being crossed somewhere. Trouble is, I cannot find anything labeled anything like "Brake Light" in any of the 3 fuse panels (under hood and dash side panels). I see headlights, turn signals, etc, but nothing for brake lights.

 

Where can I find the relay for the brake lights?

Or, does anyone have a wiring diagram that shows the path of that circuit so I can check it for shorts?

 

 

 

The second problem is bigger, but probably easier to diagnose.

The damn thing won't crank at all...

 

The On/Acc position on the switch lights everything up normally, but when you crank the key, the instrument panel goes completely dark.

When I removed the ECM to replace the broken bracket I found a small dent in the back cover. It didn't look big enough to cause internal damage, but maybe it was.

 

I also noticed that the 30A fuse in the underhood fuse box was burned out for the ECM power supply. Just another indicator that there was a major short in there somewhere. I'm just hoping that whatever damage caused that didn't also burn out other ignition components...

 

I am now trying to find a replacement ECM, which is a 2015-specific part. Its visible from ACDelco, but is apparently on permanent backorder...

Anybody have an idea for where I can find an ECM for this year? Or whether I can use the ECM from a 2014 LML on my truck?

 

 

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Brake Lights work ANYTIME the brake peddle is pressed , no mater with the key on or off or pulled out ... I'd start to see if the brake peddle switch on the top of the brake peddle arm got messed up /stuck in the on position ...

 

Best of luck ...

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