1993 Chevy Silverado Heat Gauge

Try replacing the temp sending unit. It's a cheap part, located near the t-stat housing and will most likely take care of the problem.

Let me know if this helps.
Joe

Joe is correct...there is a coolant sensor next to the t-stat housing but the main temperature monitor of the coolant is the temperature switch. You can find it under hood, on the driver side, just below the valve cover, between the front and center exhaust ports, mounted in the cylinder head. If the wires to the switch are broken or disconnected, your dash heat gauge will not work