[DrDave]

Okay, it's time to dig deep into the bag of diagnostic tricks. One thing that we want to know is whether the alternator field is actually energized. For this we are going to perform the wrench trick. Take a small (3") steel wrench and balance it on top of the alternator. Have a friend turn the alternator/master switch on. You should see the wrench move. The wrench moves when the field is excited in the alternator creating an electromagnetic field. If the wrench moves it is ready to charge. Twice I worked on charging systems where it turned out the the alternator wasn't turning. In one instance the rotor shaft was broken. The other alternator had sheared the coupling.

In the field circuit there are multiple connections. The field circuit connects bus bar - field breaker - alternator switch - regulator switch - over volt relay - voltage regulator - alternator. There can be a bad connection at any point along the way. The best way to diagnose the circuit from the bus bar to the VR is using a volt meter on millivolts between the bus bar and the battery lead of the voltage regulator. Do this with the entire circuit hooked up and energized. A number around 100mv. is acceptable. Check the voltage drop from the field lead of the VR to the field terminal on the alternator as well.

If all of that checks out you are down to checking the output circuit of the alternator. You want to check voltage drop across the alternator circuit breaker and related wiring from the alternator to the bus.

If all the wiring checks out and the wrench trick makes the wrench move you are down to looking closely to the VR

Your system may differ slightly from mine but the basic idea will be the same.

Report your findings.