You are only blowing out the tail light bulb? (if the voltage is high you would have problems with all bulbs)
What is the voltage at the battery with the car off. (A battery with low voltage at rest could indicate a bad battery allowing the generator to put out a higher voltage)
With the engine running what is the voltage at the battery? (A high voltage could indicate a bad ground making the generator put out more to compensate for the bad ground)
What is your ammeter reading when the car is running? If the battery is
confirmed good and the grounds are good but the ammeter is reading high then this would indicate an adjustment of the third brush is needed.)
https://www.fordbarn.com/forum/showt...ring%2Adiagram