Fathead

Hi all I hope someone can help out here . have a ep70 that its temp gauge is going into hot as soon as its ran for 2mins .. No oil in water no water in oil , no air in system . new thermostat , new sensor . new water pump.. So its wiring issue would someone agree ??? I ran a wire from sender direct and gauge goes straight into red without engine running .. Would someone have a wiring diagram or advise please ?? Its a 1lt boxey ep70 1985