Does the column your using have a hazard button? Could be as simple as the button is on, or stuck. If it is indeed the hazard lights your seeing, that would also indicate that the hazard flasher unit is bad, or those hazard lights should be flashing. The hazard lights over power everything else through the turn signal and brake light switches. If the hazard button is engaged, the brake lights nor the turn signals (in either direction) should work.

I know its pretty stupid, but I have to ask, are the lights you are seeing turn/brake, or tail/parking lights? You have referenced both in your descriptions. Do the lights get brighter if the brake/turn lights are activated? Also, do you have any lights on the front of the truck, particularly the front turn lights?

I had an issue with my truck right after I got it together. All the turn signals worked great. The headlights and tail lights worked great, but if you turned on the headlights and either turn signal, both of the rear lights would go full bright. I ran through everything I could think of over 4 days. I enlisted another car wiring guy, and he was as stumped as I was. What I found, by accident, was the wire harness I used had provisions for side marker lights. None were being used on my truck, but the two front side light terminal sockets were shorted out! After I cut those two sockets off, all the lights functioned correctly.

One more stupid thought, are you using LED lighting? Gene