?? can't figure out y brake light won't work. 3rd brake light does work.

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Mr_Pud

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Alight, I done some diagnostics yet no prevail.. both brake lights in rear do not work. turn signals, 4 way haz lights, running lights and 3rd brake light works perfect. starting at the rear I checked the pig tail connection and had power when 4 ways were on, but no power when brake pedal depressed. One place I did not check was the pigtail conection under the drive cab..... might check that tomo. checkes relays and fuses..I have a white wire under the dash. that is spliced into for the brake controller. I get 12 v there checked the connection there all good. I did notice however when I have key off and depress brake pedal my 3rd light comes on but I think is what is the brake switch which is attached to the top of the pedal does not click but with the key on it does click... I have done some research and a lot of write ups tend to lead to the multifunction switch. I have tried to look up a pin out schmatic but not found one yet. I want to make sure if I put 12v in I get 12v out after it runs through the turn signal switch. I assume if you put 12v in a certain pinout for the brakes you should get 12v out at another pin out that goes to the brakes unless 12v goes into the turn signal which would override the brake light which I have a feeling the over ride is some how stuck on but Idk I would think I would have constant flashes but Idk what do you guys think???

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Mr_Pud

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i guess I should of mentioned it's a 99 k3500 on a good note I did get my new tow mirrors installed... not to bad for 80 bucks

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Mr_Pud

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I fixed the problem thankx for everyone's help. I sliced into the brake wire feed that goes into the ignition switch connector harness... some reason it wasn't working...

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RonM

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I'm troubleshooting the same problem. I had previously checked grounds, checked and repaired all wiring from engine compartment back, and replaced brake light switch ($10 insurance even though old one wasn't bad). Also used test light to check wires coming out of the new brake light switch for power when pedal depressed, and that appears good. My multi-function switch was acting up already (turn signals flashing erratic blips when lever not tripped, etc.), so I replaced it today thinking it was the source of brake light issue also. Still no lower brake lights except high-mount.
When you say that you "sliced into the brake wire feed that goes into the ignition switch connector harness" to fix it, what connector/harness/wire are you referring to? Do you have a wiring diagram or picture?

Thanks,
RonM
 
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