I have a 1974 Ford 3000 (diesel) that after a few minutes of running the temperature gauge always reads in the red and beyond the max scale. I have just replaced the water pump, thermostat (192 deg F) and radiator. I have also tried two different temperature sending units both with the same results. The tractor runs at expected temperatures based on IR thermometer readings. The fuel gauge works properly and I feel I don't have any electrical issues like voltage stabilizer or regulator problems. The temp. gauge responds to differences in resistance but I am thinking either there is something wrong with the gauge or it does not match my temperature sending units. Here are some resistance readings from the sending unit to battery negative terminal. Tractor cold - 600 ohms and gauge on full cold. Gauge at lower end of red - 42 ohms. Gauge at upper end of red - 40 ohms. Tractor running at normal operating temp. after thermostat open - 28 ohms. Can anyone tell me what the ohm reading should be at normal operating temperature and at the lower end of the overheating (red) level? I cannot find those numbers anywhere in manuals or online. Thanks.