Brian, I have the connector that plugs into the headlight in my hand, with the + lead on the white wire's connector. I have the - lead on the battery ground. In my other hand is the headlight. I can barely plug in the light, and watch the voltage drop. The yellow wire I would believe to be for the low beam, since it has +12 volts on low beam setting and goes to 0 switched to high beam.
The connector does look a little green, so I'm gonna clean that when I get a chance. Last time I had the lights out I used the dielectric grease, so it could have corroded more since I had them out. They both did work since I've had the car.