Not sure what car you have, if its an 8v digi the coolant guage sensor is in front of blue ecu coolant sensor in front of head. Unplug it and short the two wires out, if the guage rises its the sensor at fault-replace. If its a 16v the sensor is a small black m10 screw in jobbie on side of head with 2 other sensors, disconnect it and short the wire straight to the head, direct. If the guage rises its the sensor at fault, if not its the wiring. If you have an 8v kjet I'm not sure where/what the sensor is like, but the principles the same, disconnect and short it to earth to see if its the wiring or the sensor at fault.