I pulled into my drive way and turned off my truck and the heater motor stayed on. I turned the key on and off a few times and blower motor kept running.

I cycled the hearter controller and and the blower went off. Next morning both batteries were dead flat!

I took the dash apart and found 11.5 volts on the brown heater wire with the key off, but 12.5 volts with the key on.

I took the fuse block apart and found that a large Orange wire and a Large Pink wire both had continuity with the heater wire. The Orange wire had 11.5 volts with the key off and 12.5 with key on. So I chased the Orange wire in the engine compartment.

I put my hand on the alternator and was superprized to find it hot!

The two wire plug on the top of the alternator was black and half melted.

The large Red wire that comes from the battery to the Alternator was rubbing through on the water seperator bracket for the air intake. I am guessing this was the culprit...

I check the pins on the alternator after removing the damaged plug and one of the terminals has continuity to ground! I assume this is bad, but want to know if any one else has had similar problems.

To futher muddy the waters, with the wires conected the alternator is charging even though it gets hot!

Any chance of an easy fix? Before buying a new alternator I want to know what each of the wires should have for voltage so I can be sure I won't burn up a new alternator!

One other thing, do diesels use different alternators than gassers? Higher amps at lower RPMs? Tach lead?

Not 100% sure, but I would expect the plug on the alternator to have one ground, one 12V and one wire for the charging light. However, I don't have a charging light, and afair one of the wires on the plug is connected to one of the other wires, and the other one is 12V. That would make two grounds and one 12V.

When alternators are charging, they get hot. Their efficiency is extremely poor, only about 50%, so they generate a lot of heat. 70amps at 14.4V is about 1kW, so it takes 2kW to drive the alternator while it puts out 1kW in electricity and 1kW in heat.

The charging wire from the alternator to the battery should have a fusible link in it. Does anyone know where you can get those?

You should have a SI-10 or SI-12 alternator, 74amps. If you have a V-belt setup, you cannot reasonably drive an alternator with more output on a 6.2 because you cannot prevent it from eating the belt.

Thank you, I understand that an alternator gets got when it is running, in this paticular case the truck had not been run at all only work on and with out running it became hot.

This morning I checked the pins and it is no longer grounding to the case so I plugged the wire back in and it now charges correctly!

I have Optima Red tops and they have reversed connections from that of the stock batteries. I did not notice at that time that by reversing the battery terminals that the main charging wire was now laying against the sharp edge of a bracket!

So this one is my fault! But it is fixed now.