Ampmeter testing?

[tomfg]

I have to pull the instrument cluster soon to fix the speedometer, install a tach, and maybe a voltmeter. I've been wondering if the original ampmeter is working at all. I never really see the needle fluctuate from center....... maybe a tiny wiggle when I turn the heater blower on. The truck has a 78 350 cid engine in it, with a internal voltage regulator alternator.

On other old vehicles I've owned from the 60's, the ampmeter always showed "charging" of several amps after starting up the car, or perhaps discharge at idle with the headlights on.

Is there any test I can do before I tear the cluster out to see if the ampmeter is working as designed?

If I turn the headlights or heater blower on when the engine is off, should I see anything happen on the ampmeter?

How about testing the ampmeter when I have the cluster out of the dash?
What should an ohm meter tell me?

Thanks for any tips.