hi guys i have a 1986 ford f350 and it wouldnt start so i put the charger on the battery it has 2 batteries and after 30 minutes on the charger at 10 amps the truck still wouldnt turn over and when i put my volt meter on the terminals the reading kept going down starting from 8 volts down to 6 volts something is draining somewhere any help would be greatly appreciated its a 460

 

Disconnect the alternator at the starter solenoid and see if the voltage drop stops.

If your batteries are down to 6V I would say the short has killed them.
JMHO...

 

Or one of the batteries has a shorted cell....which will suck the life out of everything attached to it (worse than an ex-wife).