I have a 92 chevy Silverado 4x4 and have been having major problems with my taillights! every time I turn my head lights on my running lights, turn signals, and brake lights wont work. ive looked for shorts or bad spots in my wiring loom cant see anything. I replaced my head light switch, turn signal switch, and tail light circuit boards hoping to fix the problem. the weird thing is I have some magnetic towing lights that plug into my 4 pin connector and they work!!! Is driving me crazy and would appreciate any help possible or ideas to try. also checked fuses and relays in truck and seem good. it will blink once in the dash then stop I think the head lights are drawing all the juice away from a bad connection somewhere but not sure at all.

oh yeah and only my lights in the back wont work with head lights on, up front they still work!

Welcome to the forums Travis, I am sure somebody that knows Chevy Trucks better than myself will respond, and help you with your issue.
I noticed the other thread you started before posting this one, so I am removing that thread since you'll get helped a lot easier without multiple posts on the same issue.

you clean your grounds? chassis to engine, chassis to battery, etc..

Fixed those tail lights, I checked the chassis to engine ground and everything seemed fine still cleaned them up. Found the problem at the back of my wiring harness a clipped black wire. put an eyelet on it and grounded to bumper brackets and bam everything is working again,

Great news man, glad you found the problem, thanks for updating us on your findings!