Charging intermittent, sometimes it does sometimes not

Start as if a new problem. Troubleshoot it

I treat the charging system as several sections

1...Charging path. This is the main charge line/ path from alternator output stud to battery. OEM path is output stud---BLACK wire to / through bulkhead connector---to ammeter---out ammeter on RED---through bulkhead---fuse link---to battery

2...Field path. The VR gets power from the IGN1 "ignition run" and the alternator field gets power from the same place.

VR MUST be grounded.

Alternator field current path is from ground--through VR---out on GREEN--to one field---through field---to light blue to IGN1---key/ etc/ battery

TO TROUBLESHOOT you need regular tools, a 12V test light, and multimeter, and some alligator clip jumper leads

IT IS A GOOD IDEA with a "new" / rebuilt alternator TO CHECK that neither field terminal shows continuity to ground. Ohmeter should show infinity/ open from either field to alternator case.

Remove GREEN field wire at alternator. Clip an jumper to the disconnected alternator field terminal, turn the key to "run." Check voltage at light blue field terminal, leaving it connected. Should be "about same as battery." If you disconnect/ reconnect jumper in quiet and subdued lighting, you should see and hear a small spark, showing current through the field circuit.

You can double check that by setting your multimeter up for high current (10A or 20A scale) and put the meter in series with the jumpered field terminal to ground.

If this seems good so far start the engine, with meter monitoring battery voltage

Slowly bring up RPM watching battery voltage. Try not to allow battery above 16V. If no change, move meter to alternator output stud and ground. Recheck. If voltage goes way high, the charge path is open, such as bad connection at ammeter/ bullkhead terminal. If voltage stays 12V or lower, the thing is not charging

At that point recheck that you have power to and current through the field and if so, replace alternator

IF SO FAR ABOVE causes a charge, this shows the alternator is good. Reconnect everything "normal" and recheck. If no charge, now we check field circuit and VR

With everything re-connected normal, remove VR connector. "Rig" a jumper between the two VR connector terminals. This can be done with small machine screws. This puts full battery power from key to the GREEN wire. So disconnect the light blue field wire and jumper that alternator terminal to ground. Again run engine, monitor battery, see if it charges. If it does charge, and you are CERTAIN the VR is properly grounded, replace the VR

VR GROUNDING. Absolutely MUST be grounded. Scrape around mounting holes on firewall and VR and mount using star lock washers