1994 k1500 brake lights issue

[HenryM]

1994 k1500 Silverado 350. My reverse, brake and signal lights work when my headlights are off. When I turn the headlights on my brake lights stop working but the signal and reverse lights still work. I have checked the stop and brake fuse but both are fine. I have also checked the pins in the connectors and the ground which is also fine. What could the problem be?

 

[Nad_Yvalhosert]

Defective circuit boards in the tail lights?

 

[HenryM]

Defective circuit boards in the tail lights?

They work when the headlights are off which is why I didn’t think it was that.

 

[jd33173]

Check your grounds and have a look at the wiring harness and connector. Trailer harnesses highly suspect

 

[HenryM]

I took out the trailer harness and checked the connections they are all fine

 

[Nad_Yvalhosert]

They work when the headlights are off which is why I didn’t think it was that.

Right, but if the ground path in the circuit board is corroded internally and the combined excess amperage draw of brake, parking light, and reverse together overload the printed circuit, something cuts out.
Try unplugging the 4 prong connector at the tail light and retest your lights.