In 1999 the fan controls don't use the other temperature measurements, like in the head, etc.

If your thermostat is opening correctly but your radiator is blocked, the small amount of cool water from the radiator shouldn't make the fan-switch cold. There's too much flow of hot water from the engine's water jacket.

Check your radiator for flow blockage. With both hoses disconnected it should easily flow as much water as you can get from a garden-hose. You can flush it that way (both directions) then rinse the whole system with distilled water before refilling.

After that, you can put it together with a new T-stat and see. If you later find you want to replace the fan switch, you can do that quickly and only lose an ounce or 2 of antifreeze.