Go to the library and get a Chilton's Repair Manual for your year Plymouth.
i had the exact same problem with our 91 voyager, i cleaned the battery terminals and the problem went away immediately
if you're talking about the stock gauges as in the tach or speedo, two options one stretched or pinched cables, two if your talking about the misc. bs lights that pop up as gauges probably a ground
The check gauges light comes on when one of the guages is out side of the safe zone. It could be battery voltage, oil pressure, engine temp....
Full diagnostics at: http://www.4x4wire.com/jeep/tech/electrical/gauges/
You need more than a diagram. You'll need a manifold gauge set, and the know-how to determine what the numbers on the gauges are indicating is wrong with your AC system.
You need a set of gauges and a can tap and several cans of R134. The low preasure connector is on or close to the receiver dryer.
It is just a thin 'sheet' that fits on the back of the cluster & has a plug-in attachment. I have a 70 RS/SS, rebuilt from ground - up. I never liked all the gauges all over the place so I wanted all the gauges in the dash - got mine at a local junkyard :) *Skylla*
The fuse will be under the hood in a black box of fuses the lid of the box will have a diagram on the inside.
Probably a bad ground; they are some times more than one ground too, check them all; make a new one if you have too.
You might have a bad ground wire,you will need a wiring diagram to find location of grounding points.
C. Temperature and Sanitizer Gauges
Check the gauges. One or more of the gauges must be out of normal range to trip the "check gauges" light.