eng off/ign on see if the blue feed wire out from the bulkhead has fire (1) at the blue wire alt field terminal and (2) at the top terminal in the VR triangle w it facing up like a pyramid (some C bodies are sideways or upside down). Pull alt brushes & quick visual of them & they wear at an angle so replace them at that same angle. Check VR ground (jumper wire w alligator clips) 1 clip to known good ground then scrape the VR case w the other clip & see if it starts charging (eng running). pull a batt cable & w your VOM see if continuity between the ends of the green field wire (alt/vr). Full field the alt: pull both female field terminals off & jump from batt positive to either male alt field terminal, start eng & at a fast idle then jump from the batt neg post to the other alt male field terminal for 3 seconds MAX & if it charges (you'll hear it kick in & slow the eng down slightly but decisively) the alt is good. Have no light bulbs or accessories going when you "full field" and it's a good idea to run a seperate 8 ga jumper from the alt "batt" terminal to the battery positive post when you full field. If the alt tests good and the blue/green circuits are good and the reg has a good ground that only leaves the reg as the culprit