80Series Temp Guage gone?

have you disconnected the speedo. sometimes that plays havoc with instruments

These guages work on a variable resister....the sender changes the current flow depending on the temp at the guage...it will either be if you remove the sensor wire off the guage should be open circuit and be below zero...ground the wire to the block and it will show full or max. The variations in temp are between those two.

Now the guage can work the opposite was also....full when disconnected and Zero when grounded.

You first need to find the sensor...Thermostat housing is the first place I would look. Small brass nut with a spade terminal conection coming out of it...
Pull this wire off and with ignition on look at the guage....full or zero? Then ground the wire it should be opposite....Zero or full.
If this doesnt happen the guage is shot (or you dont have right sender) but if it does go from full to Zero or vice-versa then your guage is good and then sender is shot.

There are instances when bad/intermittant supply behind the dash causes guage faults too.

This is just a quick check to see where to look!!
Goodluck with it Bernard.

Matt.