You're right, that won't work, since the light only tells if the output
of the gen/alt is system voltage or much less (then it lights).
An ammeter is tricky to hook up and requires pretty heavy wire since ALL the
current flows through it. Also if you get a short in it you are dead and may
also have a fire. A Voltmeter is a lot safer and gives you just as good a
bunch of info (at least in terms of usefulness). Does not require heavy
wiring and can be hooked to almost any "hot" point in the system.
I have an ammeter in my 164, with which I burned all the insulation off a
couple big wires when one contacted an exhaust pipe. Sure filled the car
with stinky smoke when the wire turned red! I'll take it (and its "new"
wires, installed in 1976) out when I work on the dash and put in a voltmeter.
I realize that this is a bit late....
--
George Downs Bartlesville, Heart of the USA!