'00 silverado trailer electrics issue

Got a problem with the trailer wiring on a 2000 Silverado that seems to be defying the laws of electronics. Have a standard 3 to 2 wire light converter on there that I had assumed had gone bad, because all the functions/lights are working properly, when when the brake input wire is energized, there's no output from the converter to the trailer. Turn/park light functions however work fine. Installed a replacement converter today - same problem. Did some further messing around and found that: -The turn signals/hazards all input AND output properly -Tail/running lights work properly (truck and trailer) -If the truck's brake lights are on, the brake input to the controller gets 13.2v, but there is no output to the trailer lights -If I use my probe and supply 12 to the circuit just before the converter, the truck's brake lights come on and there's still no output to the trailer. -If I disconnect the converter's brake input from the truck and give it 12v from my probe (Cig lighter) there is output to the trailer brake lights Now, I'm scratching my head a bit at how voltage from one circuit could make it work, while another wouldn't. Unless one was starved for current, it shouldn't matter. Anyone seen anything like this before?Best Buy 465

GeekSquad AutoTech - MECP Advanced Certified

The most common cause is a bad ground. Verify all grounds at the vehicle and the trailer.

Does it have the factory tow package? Does the third brake light work? For some reason GM wired the trailer circuits all funky. The 3rd brake light is part of the trailer circuit, not the stop lamp circuit. If your third brake light does not work check the fuse and see what that does for you... This is all assuming it's wired the same as my 2004 2500hd.-Chris