Electrical Gremlin?

Pull the instrument cluster out and make sure that the wires are ok. I had a 69 valiant where the insulation somehow got melted off of the main wire from the battery feed of the alternator that feeds into the alt gage. The wire would then short out to the dash frame when going over bumps/ets. I was putting alternators and voltage regulators on it every six months until I found this and replaced the bad wires. Then never put another one on again after I got it fixed. It would not always short out, just here and there...