Re: Wont Start.....Electrical Problem!!!!
Put the batteries on a slow charge. Preferably, charge each one individually by separating them in the circuit. Check the battery voltage after charging. Check each battery, with them separated from one another. Should be 12.5-12.8V, with the two being fairly close to one another. Start the truck, run until the glow plugs have cycled off and check the voltage. Should be 14-14.5V.
Next time you park it, disconnect the negative cables of both batteries, and check the battery voltage again, and note it down. Hopefully it'll still be 12.5-12.8V. After the truck has been parked for several hours, go out and check the battery voltage on each battery again, before reconnecting them. If the voltage of either or both has dropped considerably, the batteries are not holding a charge and should be replaced. If the voltage has stayed pretty close to the original (at least 12V), then there's a good chance you have a parasitic load. If you have a voltmeter with a high enough ammeter measurement capacity, you might be able to measure the parasitic load and chase it down.