JBCOBRA JB you belt is loose or you but some sealer on it like a belt dresing. It is causing the belt to slip and grip. When it grips the gauge pins, the regulator stops charging and the gauge drops to protect the system. And goes back and forth. Try getting some fine sand paper and sand the inside of the pulleys where the belt rides, alt too. Then clean these places off with brakekleen. I would get a new belt because you cann't get the silicone or wax off the belt and out of the pours of the rubber. Try this. If the gauge is still pinning you have either a loose connection to the battery or you have wetted the Alt and possible damaged the internals. I would say with out seeing it you cleaned the car too good.
Rick L.