cluster gauges not working.

I owned an 87, still own an 86, so I have some manuals. But......they aren't much help

1 Be SURE the ammeter is NOT working because it is completely separate from the fue/ temp/ oil

Test again carefully, using headlights, and watch for any movement. These ammeters are known for being "numb" IE not moving very much. Take your voltmeter when running and check the battery voltage. It may not be charging. Should be close to 14v, or if the battery is going down from not charging, should show at least 13

2 My Haynes, Chilton manuals were no help. I have a Ferd "shop" manual, but it's missing the main schematics. I did look at the simplified diagram for the fuel/ temp gauges, and they are the same

It shows comes off the IGN SWITCH - an IN HARNESS 8.5 ohm resistor -- to an IVR (just like your Mopar instrument voltage limiter -- to the gauge -- to the sender

There may be a fuse, not shown.

It APPEARS that the gauges MAY get power off a separate terminal on the IGN switch, so it might be you have switch problems.

What you really need is a complete wiring diagram. I don't have anything that shows what color or terminal out of the IGN switch supplies the gauges.

I think I'd pull the cluster out and check the IVR

IF the ammete truely is not functioning, it might be a separate issue, or it might be bad connections in the ignition switch or other "common point" that supplies both the regulator/ field, and the gauges.