6x4 Diesel Gator Overheats

2004 diesel gator starts and runs as expected. Unfortunately, radiator fan does not come on and engine overheats. Fan has been tested and works. Fan switch in the radiator has been replaced. Thermostat has been tested and works. No obvious leaks in the system.

Water pump does not show any signs of failure (noise, leaks or vibrations).

I am out of ideas and appreciate any suggestions.

Thanks

GatorJ