I just installed a gauge recently too.. The dimmer is wired strangely and requires the 'lighting ground' wire, use the light wiring off the Cigar lighter, its alot easier to make sense of.. don't just ground the light, it won't dim.. use the black (with yellow tracer????) lead from the cigar lighter as the ground for the light.. If you need a good ground for the gauge itself, the metal bracket under the dash that attaches to the steering column has the least resistance that I've found in the passenger compartment..