voltage pulse

My 67 has later isolated field 60 amp alt' and solid state regulator (approx' 8 feet of blue wire added to the 67 harness). Those parts were taken from a 73 model donor laying here. Also mention Alt' gauge converted to volts gauge. Some time later, when the volt gauge suddenly presented a pulse, regulator was suspect and not going to break my bank. So I didn't attempt any diagnosis. New regulator cured it.