Third Brake light only works with interior lights

[robbin'thabanks]

I have a weird problem with my 94 k1500 ecsb and the third brake light only works when the dome light switch is on. I tryed tracing the wires from the third brake light as far as i could and didnt see anything out of ordinary. Any ideas where i can start?

 

[Mean Green]

Are you talking about your cargo light in the third brake light? Or the running/brake light itself? Also do you have your cargo light switch on?

 

[robbin'thabanks]

no i mean the brake light in the third brake light, the cargo lights work on their own switch. Its the guage dimmer switch, i turn on the interior lights and the third brake light works

 

[CodyB]

When I tried to install a different light in mine, I could not run the brake light and bed lights off of the same ground. There's four wires and they need to make the correct connection between them to work right. The cab lights are a switched ground I think, and the brake light is a switched positive. I may have those backwards.

I hope that may help, Are you installing an aftermarket housing or LED brake light?