I would concur with everybody else on checking your ground. On my toys, since I like having all my gauges to work, I always add an additional, dedicated ground wire to the cluster. As has been said, bad grounds can cause all sorts of weird problems. I once saw a '69 Fury that had such dodgy tail light grounds, that when you turned the hazard flashers on, the tail lights would alternate like a cop cars' wig-wags!