Gocart879,
I will take a guess. The plate is a 'shunt', and is wired as it should be in series with the alternator output (through the regulator) and the battery connection on top of the starer.
The in-dash ammeter is only taking a sampling of the system activity. This setup would be considered a tad more modern, and a little safer in that the ammeter inside the cab doesn't have to act as a conduit for the entire trucks current flow.
Voltage would be read with a voltmeter. Amperage, or current flow must be read with a ammeter. This must be in series with the load, or a inductive device must be used around a wire.
The ammeter will not move until current flows through it (the shunt).
What values are on the ammeter inside the truck? Some gauges might be -60--0--60+ or -30--0--30+.
The gauge, being on a shunt, might not respond to small amounts of draw, but might respond to a charge of 40 amps...who knows.
I didn't think the truck had the alternator in it, so troubleshooting it now isn't a viable option. The gauge could be stuck...when everything is reinstalled, flick it with a finger and see if it starts working.
Stuart
