Stuart,
Before I read your response, I tried to check the amperage and realized that ACA probably means alternating current amps. No setting for direct current amps on the multimeter so you is right. It would be nice to be able to see what the flow of amperage is would it not? Even though it seems to be working fine, not sure I completely trust the truck's ammeter. Anyways, it doesn't give you an exact reading. You just kinda know that if it's not in the center somethings wrong...
Tanks, Skip