Temp Gauge not working

[1968CHEVYC10]

Well I think the gauge may not be the problem, but it never moves when I'm driving it. the gauge will peg hot when I ground the wire, So I replaced the temp switch, didn't fix it. I tested the temp with a multimeter, put the +lead on the + side of the batt, then the -lead on the spade connection on the temp switch, read 12v. From what I've read this means the switch is short circuited and no good, but then shouldn't gauge peg hot when ever the wire to the gauge is hooked up? It doesn't.