Need help with going back to stock set for mustang alternator. I have an old school alternator on my car with an after market March bracket. I put a new battery, external votage regulator, and replaced the alternator with the exact same old school alternator only to find that one I fire up the car my voltage is showing 12. Someone has spliced in new plug in for the alterator. I have only three wires going to the alternator and would like to go back to factory hood ups. Could the gage be off?