Gocart879,
Without getting too complicated, I think you should hear a "click" from the regulator when the key is turned ON. It might be slight enough that you have to hold your ear to it (the regulator), or hold a screwdriver to it while 'listening' to the other end.
The regulator needs to 'click' a relay closed to feed voltage to the alternator in order for it to charge.
This is a basic requirement for a conventional externally regulated system. As I mentioned before, yours doesn't appear to be conventional, but should still have some of the same basic characteristics.
If this type of system is indigenous to emergency apparatus, maybe checking in with a forum specific to fire engines could be worthwhile.
Stuart
