Drivers side low beam headlight

Low beam wiring has twelve volts on the two wires going to the low beam head light. When you hook the power wire to the bulb and and the ground to the outside connection point to the bulb we get zero volts. If we test with a voltmeter and disconnect the ground from the bulb assembly and put negative terminal from voltmeter directly to the ground wire, but leave the hot power connected to the bulb we get twelve to thirteen volts.