Brake light grounding

[papapavs1]

Hello, 1978 GMC K25 fleetside. After doing quite a bit of work to the truck, I now have no brake lights. I did a new ignition switch, ignition lock cylinder, and had the box pulled a few feet back for paint. All lights worked fine before this. Tails and Turn signals still work fine. I jumped the brake switch and I have 12v back to the socket. I cleaned up the ground behind the drivers light housing, and even added a ground from the box to the frame, still to no avail. I also unplugged the rear wire harness at the firewall and ran 12v straight from the battery to it to eliminate it possibly being a turn signal assembly issue. Reviewing wire diagrams shows that the ground behind the drivers side housing is the only ground for the lights back there

 

[Tom Weeks]

Hello, 1978 GMC K25 fleetside. After doing quite a bit of work to the truck, I now have no brake lights. I did a new ignition switch, ignition lock cylinder, and had the box pulled a few feet back for paint. All lights worked fine before this. Tails and Turn signals still work fine. I jumped the brake switch and I have 12v back to the socket. I cleaned up the ground behind the drivers light housing, and even added a ground from the box to the frame, still to no avail. I also unplugged the rear wire harness at the firewall and ran 12v straight from the battery to it to eliminate it possibly being a turn signal assembly issue. Reviewing wire diagrams shows that the ground behind the drivers side housing is the only ground for the lights back there

 

[Tom Weeks]

Tray cycling your four way flashers sometimes the switch gets pushed part way in.

 

[Ricko1966]

It's not a ground if tail and turn work.