Ammeter discharge with key on

67Dart273 said

Gauges draw less than an amp, I think. In any case, the gauge (temp, oil) would barely be noticable on the ammeter.

Good point about the ammeter, though. Make sure the "reading" you are "reading" is not the "natural" off center it might have when off. It's why I insist you MUST use a multimeter that is fairly accurate, at least, to see what you "really have" there

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With the original mechanical limiter and during initial switch on ( warm up period ), the current flow is relative to the fuel level.. That limiter will pass as much current as it can until the needles reach intended positions. Afterwords the draw is reduced.
I guess the most severe draw at switch on I've seen would be a internal short at the alternator. Easy test is just pull the blue wire off of it.