Hi I had a simular problem back in the mid 80's before I knew better. I converted my 53 club coupe to 12 volt and burned the gas gage out. All it takes is a small resistor I don't remember the resistance if I find the extra ones I have I will send you the numbers. The oil and the temp gages are not affected and the amp gage worked on mine did not affect it. the resistor goes right to the gas gage itself, or to the hot wire so that it wont burn the gage out. It would be simular to the heater motor. If no resistance to the heater motor then the motor will burn out quick,be careful. check it with a 6 volt battery first and if it still works put a resistor between the fuse and the motor. I believe that you need a resistor in your line to your points to keep them from burning out, as well. My 53 ran great until one day I was at a stop light and it would not start after it dyed. It was the points had burned closed. Live and learn right. I also have a 54 GMC but it is in boxes and I dont know if all the gages are electrical or not if so I am sure you need resistance. I hope this helps some good luck.
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