brake light issues

[hilly101111111]

I have a 1990 GMC K2500 350/Turbo400 trans 4x4 8' bed. Every time I hit my brake pedal when the headlights and tail lights are on, my drivers side tail lights go out and my backup light lights up. Also when the lights are on and I use my driver side turn signal the tail lights and the backup light flash and alternate!
Ive been slowly going over my grounds as well as the harness in the back is new and each side is grounded. I have new boards and bulbs too. I also have new brake light switches and a relay for LEDs. Any help would be greatly appreciated !

 

[jd33173]

Unplug that rear harness, break out the test light and test each function one at a time. Double check those grounds and ensure they are actually grounding. Check your lighting function one at a time - parking lights, head lights, get a cup of coffee, an open mind and be deliberate. Look for hacks or splices, go step by step

 

[GoToGuy]

You installed a new harness then the problem appeared? Was there any problems before the harness change?
Have normal brake lights with headlights off and headlights on? If so and the harness wiring matches oe colors I'm thinking it's somewhere up front. Turn signal stalk , crossed, shorted wire. The turn signal is also the brake filament. To get the backup light on turn selection has to a short or cross up front.

 

[hilly101111111]

yeh started before the harness change. I noticed all of this when my brake light was out and for some reason that new crappy TYC board was no longer working.I replaced the board and the bulb that didn't work. ill double check all my grounds and go threw the wiring in the back again. I had checked the voltage at the tail light after all of this and its not quite 12 volts however my multi meter is kinda junky. it must be a ground issue bare wire or that turn signal stalk. I was thinking its under the dash and or in the column. I have been going over all of my wiring taping and looming it. The original owner added wiring for random things here and there but I basically removed it all and now the harness in the back is replaced. When I get a day off work again I will go over it all back to front again and go from there. Im not actually sure what light is the actual brake light but when the headlights are off and I step on the brakes the middle and top bulbs both light up lol I don't think that's correct. Thank you guys !

 

[Keeper]

I think there is a ground wire to inside of frame way back on the driver's side

 

[hilly101111111]

I think there is a ground wire to inside of frame way back on the driver's side

ill look around !

 

[GoToGuy]

Did you download the service manual PDF her in forum there free. In a sticky above a thread with the links to the library of OE service manuals. In the electric section has wire diagrams. Truck diagrams with wire loom layout , ground locations. Wire digrams and circuits complete. I have purchased new complete TYC twilight assembly. Three pair so far, two trucks and Tahoe, and have had no problems with them. It cheaper to buy a whole assembly, even comes with new bulbs installed. Especially if red lenses are getting hazy.

 

[Schurkey]

Perhaps a moderator will move this thread out of the ENGINE section, and into Audio + Electronics.

 

[hilly101111111]

Did you download the service manual PDF her in forum there free. In a sticky above a thread with the links to the library of OE service manuals. In the electric section has wire diagrams. Truck diagrams with wire loom layout , ground locations. Wire digrams and circuits complete. I have purchased new complete TYC twilight assembly. Three pair so far, two trucks and Tahoe, and have had no problems with them. It cheaper to buy a whole assembly, even comes with new bulbs installed. Especially if red lenses are getting hazy.

ill have to download the service manual PDF ! Thank you