So you ripped a wire out and now it won't work? Did it work before the wire was ripped out?
Put the fixture back together (with a known good bulb), grounded to the case just like you have it now. It looks like the metal socket is affixed to the metal case so grounding the metal case should work, unless the socket is isolated from the case with rubber or fiber washers. A simple continuity test would confirm whether the socket is grounded to the case.
Touch the wires directly to the battery, black to ground and red to positive. This will test one filament. To test the other filament touch the black to ground and then touch the yellow to positive. This will provide a definitive test for the light only and prevents any confusion that might arise based on a faulty switch or faulty wiring. Then when you hook it up to the harness you'll know the light is good, so if it won't light when connected to the harness you'll know you're looking for a faulty switch or faulty wiring at that point.
