1999 Tahoe truck turns on when brake pedal is pressed

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mhill58

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Hey everyone I have an issue I've never seen before on my 99 tahoe, I purchased it and the previous owner told me the brake lights didn't work from a trailer brake short, the 3rd brake light works fine, when I started digging into I ended up replacing the rear light harness and cutting out the trailer wiring, and removed the brake controller, I also replaced the multi function switch as it was broken, when I went to test the brake light with the key off, everytime I press the pedal the truck turns on like I turned the key even though the key isn't in the ignition and if I do turn the key on, the brake lights stay on with out any input for me. I've never seen this before and have no idea what could cause it. Any help would be greatly appreciated!
 

OR VietVet

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Your brake lights have power all the time. You have a power feed wire, for the brake lights, that is crossed/rubbed thru at an ignition wire, likely in the steering column area, where you did all that work. If you did not have a problem, did some work and then have a problem, recheck your previous work area(s).

Welcome to the forum from Oregon.
 

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Hey everyone I have an issue I've never seen before on my 99 tahoe, I purchased it and the previous owner told me the brake lights didn't work from a trailer brake short, the 3rd brake light works fine, when I started digging into I ended up replacing the rear light harness and cutting out the trailer wiring, and removed the brake controller, I also replaced the multi function switch as it was broken, when I went to test the brake light with the key off, everytime I press the pedal the truck turns on like I turned the key even though the key isn't in the ignition and if I do turn the key on, the brake lights stay on with out any input for me. I've never seen this before and have no idea what could cause it. Any help would be greatly appreciated!
go back and check your work again.
 
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mhill58

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Alright I will check it tomorrow and post my findings if anyone has any electrical diagrams of the wiring, it would help alot, thanks guys!
 
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mhill58

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Thank you for that website it helped alot, I finally figured it out after checking every wire under that dash related to ignition and brakes, I got fed up and went to my other tahoe that the frame rotted out on that I'm using as a Daily till I get this other one up and running, and swapped out the switch and there is no issue brakes work like they should. So something is wrong with the multi function switch I purchased more then likely the wires are installed wrong.
 

OR VietVet

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Yea, that does make sense. You have brake light circuitry routed thru the turn signal system, so the brake lights work when turn signals are on. What I should have caught, was you saying "truck turns on like I turned the key" but you did not say the engine turned over or started. Just that it turned on like you turned the key to maybe accessory or run position.
 

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