I don't know of any online source, but the "D" used a 6 volt positive ground system. It used a generator with a regulator bolted right on it. A quick test to see if the generator will charge is to use a jumper lead to ground the field terminal. The field terminal should be marked with an "F". That bypasses the regulator. If it charges with field grounded, then the generator is good and the regulator is bad. If it does not charge , then the generator is not charging, and needs to be rebuilt or replaced. Anytime a generator or regulator is replaced, it needs to be polarized. Do this by momentarily touching a jumper wire between the BAT terminal on the regulator and the GEN terminal. Good Luck!