[TBONE1964]

That is a mystery to me too. I don't think any system in the truck would survive 20-25 volts. What ever had that kind of voltage to it would certainly have a melt down. All of the fuses would blow also.

When you say both sides of the ballast resistor have 20-25 volts, that defeats the purpose of the ballast resistor. On a normal 12V system the ballast resistor would be used to drop the voltage from 12 down to say 5 volts. So it would have battery voltage (12V on one side and ruduced down to 5 volts on the other side. This was used on early point style ignitions because the points would burn out quickly with 12V and were much more reliable with 5 volts.

Are you absolutely sure you are reading the meter correctly? Unless you have a voltage regulator stick open, you would never see that voltage number from a 12 V system. You may see 16 to 17 and then things would start melting and fuses blowing.

I would check it with a different meter just for reference.