Project "Chihuahua" '65 Formula S Restoration "Estilo Mexicano"

That 5v pulsing is from the IVR on the back of the circuit board, and is normal. The gages read at roughly 5v and the cheapest way for chrysler to do this in 1960s tech with a 12V electrical system is to make a pulsing instrument voltage regulator, and design the gages to respond slowly so the needles dont jump with the IVR unit pulsing.