Has anyone connected a standard four pin plug to a 97 Blazer? There is a factory pigtail from the wiring harness at the rear of the truck that your supposed to hook a trailer light plug to. I've gotten the turn signals and brake lights to work when the running lights are not on. However, when I turn on the running lights, the turn signals work but pressing the break pedal causes all the lights to go off. The voltmeter shows a negative charge under this condition - Why?
Green - Right turn signal
Yellow - Left turn signal Brown - Brake lights
White - Frame ground
A test light might be better for hooking up trailer lights than a VOM - it takes out the guesswork about polarities and negative voltages and stuff like that - it's either on or off. Hook the wire on the test light up to a good frame ground. I would then disconnect the pigtail that you probably have wired in already and probe the wires with a test light until you find out which wire is which - turn on one turn signal... probe until the light flashes... then connect it to the proper wire on the pigtail as I listed above. Repeat with the other turn signal... then the brakes, etc.
<font color=red>TOO MUCH POWER</font color=red> isn't enough.
Sounds like a bad ground to me. Check all the grounds and make sure the are good and tight and also that they are on bare metal, even remove some paint where it is attached to get a good connection. Did you try hooking it up to another trailer? this would eleminate any problems with your truck.
Good Luck with it