hi guys
my neighbour has a problem with charging circuit . the alternator has 4 wires going to it, 3 to plug ( 2 x 12v + indicator) and 1 to a stud bar which i assume is connected to diodes. He advised me that his indicator light on instrument panel has not worked for sometime (could be blown lamp) Can anyone explain the voltages expected at each terminal with ignition off, on, and with engine running.

thank you kindly