After fighting with this all weekend and having read over many posts that say white wire on stock 97 tail light harness is a ground wire and having always believed same myself, I hooked up an unused orphan factory white wire at rear of taillight harness to ground (although I had wired trailer harness with white to ground on truck frame separately also) and immediately started blowing the brake light fuse (also powers hazard lights and door chime). Also when brake controller was activated by pressing override button on it, the headlights dimmed and voltmeter dropped to about 9 volts. Shorting somewhere though only fuse that blew was the brake light fuse (#1). So I disconnected the orphan white wire again and tested it. It is hot only when brakes applied. Have seen so many posts advising this wire at rear must be a ground that thought I should post this to correct that common but erroneous conclusion. My Suburban had the factory orange and blue wires in the harness too (not connected at front or rear) as they delivered these trucks. Not sure if Tahoe Yukon Silverado in 97 are the same but good chance they are. So, if you have a 97 that is blowing fuses to brake lights after hooking up trailer wiring - that white wire in stock taillight harness with factory tow package wires bundled in is a brake activated hot and not a ground. I used the orange heavy gauge wire to charge battery that powers trailer winch and of course the blue heavy gauge wired goes to brake controller at front and to trailer brake circuit at rear. Don't know why GM would not have just run this white wire into cab to use for brake controller instead of having to hunt through the myriad white wires coming off the brake switch to find the cold side of brake switch to hook into controller, but I suppose they had their reasons. So my white wire on trailer goes to frame ground on truck with usual white wire, but the white wire in harness at rear is NOT a ground and looks to be hooked to 3rd brake light on some GM trucks of this vintage, though not on mine. Hope this saves someone the headache of trying to sort that out..