Electrical connections are tough.
I have an old 2-year electronics degree from the community college, and I can tell you, auto/motorcycle electrical problems are frustrating, to say the least. I would say look for a bad ground. You say you can find +12 volts with your voltmeter, but where are you grounding the voltmeter, to the frame? In both of the connectors, find the pin that goes to ground (to the frame), and check for continuity to the frame. In all the wiring on the bike, the frame is the ground, but there's always a wire running to everything that is ground also, because the copper wire is a better conductor. Try loosen the wires where they connect to the frame and sand both surfaces clean. Good luck, and Rock On.