[Bob Lincoln]

Are there any other issues with the vehicle? Does everything else work? This is an ammeter, and C and D stand for Charge and Discharge. If they don't move at all, under any conditions, that should mean that no power is flowing through the gauge. That should also mean that most or all systems don't work. Turn the headlights on with engine off and the gauge should move toward Discharge.

It could also mean that someone wired around it, as they were often troublesome. Might be best and easiest to install a voltmeter.

 

[ImperialCrown]

Bad connections on the gauge-to-cluster circuit board were common. Disconnect the battery and remove the cluster. Spring terminals can be cleaned and tweaked so they offer better contact between the coppers. Tighten terminal nuts, if applicable. I'm sure at this age that there is tarnish and oxidation at the connector and gauge contact spots.
I have jumpered and soldered ammeter terminals to the incoming connector for proper needle deflection. You might want a service manual if you can't find pictures on the internet.
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[jamescurtis]

Living in Canada makes ebay purchases expensive. I'll be in California this summer, if the van works out, and I'll purchase a shop manual then so I can dive into the things that I need more details for.

Thanks for the feedback though. This might be one that simply gets replaced with a voltmeter.