Alternator

#1 terminal can be connected through an 'idiot lamp' to an ignition-switched battery source, which will then indicate if the alternator is charging or not, and has the added benefit of starting alternator charging at lower RPM's. The lamp supplies a small battery current through the 'Idiot lamp' to the regulator circuit/alternator field to start the charging process. Then, as the alternater starts to charge, its internally generated 12V to #1 is about the same as the battery voltage and the lamp goes out since there is little or no voltage difference across the lamp. I've done this on a replacement GM-type 'one-wire' alternator on a tractor already equipped with an 'idiot lamp' and it worked just fine. Some 'one-wire' units may be different, I just don't know.

Note: A circuit added to #1 terminal must be switched on/off by the ignition switch, else it will drain the battery over time.