My Uncle has a Farmall Super A that has been converted to 12V with an alternator. Ever since he has owned the tractor he hasn't been able to get it to charge the battery. He's but 3 different alternators on and it wont charge the only way it will charge is if you override the governor and its screaming then it charges at 18V. But if you walk up to the tractor with a multi meter the needle starts jumping across the meter when your 2 feet away it goes from 2-20V it just goes wild. This tractor does have a distributor,could the voltage somehow be getting through an insulator in it causing this wild power. What could be the problem here? Thanks in advance.