shant

Having a problem with my girlfriends 2005 Equinox. Passenger side high beam works but low beam does not. Changed bulb 2x, no luck. Socket was cracked and 2 wires showed some corrosion, clipped wires and bought a new socket and installed it. Still same problem. Used a volt meter and can not find a difference between passenger and driver side either with lights on or off. RH/LH Headlamp fuses under the hood are OK. I am at a loss as to what it can be.

Can anyone tell me how these dual filament bulbs work? Seems like what appears to be the ground for low beam becomes energized when the high beams are on. Are the 3 wires wired in some sort of phases that switch? I had originally thought that one would always be ground and the others would be hot. I guess thats not it?

Any help would be greatly appreciated. Don't really want to pay someone $70/hour to fix this.