After market temperature gauge

[SeamusF]

I know nothing about car mechanics. I recently purchased a 67 moggie with an after market temperature gauge. I ran the car with a little less water in the rad than i should and the gauge went high. Now that i have put the coolant in, the gauge is still high. I assume it is stuck. Anyone know how to reset?

[geoberni]

Partly depends if it's an electrical gauge or a bourdon tube gauge.
Is it a solid but bendy metal pipe to the gauge, or a singe electrical wire from the Sender.

Either should respond to a gentle tapping if it's just the needle stuck.
The electrical gauge can be more easily taken apart.

[simmitc]

Do you mean that the gauge is stuck high, or it returns to low and then runs high after the engine has been running? Also, does it have a temperature scale or just a blue-black-red scale and the needle is in red? If not stuck and does have a temperature, at what temp is it running?