I'll try to clear the mud as I understand it. The truck has a 24V starter on it. This is handy when you need a jump start through the NATO Slave port on the front. The Glow Plugs are 12V but wired stock they feed through a resistor bank located on the firewall behind the air filter housing. Alot of people wire the glowplugs to bypass the resistor bank and pull exclusively off of the front battery. Since each battery has it's own alternator, it balances out. The rest of the truck is 12V and I can attest to that. Put an M105 behind it that has 24V bulbs in it. Notice how dim you're bulbs are. Put the same trailer behind a Deuce, trailer lights are bright again. Even the lighting and trailer wiring is 12V and in my case, I have a 12V CD player installed pulling power straight from the fuse block. The only thing 24V left on my truck is the slave receptacle and the starter. My thinking being, if it's real cold out and the truck is dead, I'll let the front battery try and charge and then start it with glow plugs or I'll do as I did when the glow plugs were dead. Crank Crank Crank till it start's clacking and trying to catch and put some throttle to it.