I have a 1990 Ford F350 7.3 Diesel if you unhook both batterys will the motor keep running off the alternator mine stops. Thanks Curt

 

NEVER DO THAT. When you unhook the batteries the alternator says oh ****, the batteries are completely dead and it MAXES out. Which will kill the alternator, if it wasnt alread dead. The alternator needs switch power to make it work. Fully charge the batteries and check the voltage with the truck running. it shoud be around 14.4-14.6 after the glow plugs stop cycleing. And go ahead and look at the wireing harness at the alternator, there is a metal clip that always rubs a wire and shorts out. Hope this helps!

 

Right now I am getting 18 volts to my batterys with the truck warm and running Had the alternator checked at 3 parts stores and they all said it was over 13 volts. have a new regulator, new wire coming from the solenoid to the large post on the alternator. put + end of meter on the big post of the alternator and the - end on the engine block same reading 18 volts. new plug on the altrenator and wires to the regulator.

 

18 volts is way over charging. replace alternator 14.6 should be the most it should charge.