If you short the wire at the sender the guage should rise to full hot. Dont leave it there long or you could burn out your gauge (assuming it is a 1 wire sender). The temp guage works just like the fuel guage. Same resistance range etc. 10 ohms = full or full hot. 72 ohms = empty or cold. This will tell you if it is the sender OR the wiring or guage or gauge voltage regulator
