Temp Guage And Fuel Guage Problem

sounds like you messed up the grounds on the circuit board or wiring somewhere

Take it apart and look carefully at the copper contacts on the plastic circuit sheet. Make sure that they haven't come loose from the plastic circuit sheet and are not laying off to one side or the other. This is especially important for the slide contacts where the wiring connectors mate with the plastic circuit sheet. Some super glue carefully applied to the back side of the copper strips can the used to glue them back to the plastic circuit sheet.

Be sure that the anti-slosh/instrument voltage regulator module is installed correctly.

The coolant indicating full hot all the time means that you shorted the coolant temp sensor wire to power or ground somewhere.

See http://www.stangnet.com/tech/cluster87-93.pdf for information on the cluster connections and wiring differences between model years. The clusters are interchangeable, but you have to do some trimming & move some wires.
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Here's some help in the radio wiring department...

Hey pm me. I took the guts out of a 90-93 cluster and only used the 140 speedometer. To do a 85 mph to 140 mph swap