Thanks for the input guys. I checked the voltage with engine on, heater, headlights, etc on, and it read about 13.25v. With accessories off, it read about 13.75v. What should the running voltage be? Also, I checked it at the battery terminals, should it be checked right at the alternator?

91 SR5 Xtra Cab, 298000km, 4" lift, 56" rear springs, 33-12.5R15 BFG Mud-Terran T/A KM2.....and an '85 axle still waiting to go in.