Mike G.
You probably couldn't find a single soul in a auto parts store that has ever seen a generator. A shop specializing in auto electrical would be your best shot. The generators are pretty basic and easy to fix. If they haven't cooked the commutator or burned a field coil they can be tuned-up for dollars.
The generator probably could use new brushes and a light sanding of the commutator, but again, the problem could be somewhere else. If the truck has a ammeter, this would be the first step. Let the 'on board diagnostics' tell you if the generator is even charging. Look at the battery, it needs clean cables, water and shouldn't be over four years old.
A faulty voltage regulator or a broken wire will not allow the generator to charge properly. Even a loose fan belt will do it. Lots of stuff to look at in the search for the culprit.
Stuart
