Cooling Fans don't work

The cooling fans don' work on my '94 Deville, but when I unplug the coolant temperature sensor they come on. I put a new sensor in and yet it doesn'twork. What could cause the fans to not work plugged, but work when unplugged?

Whenever you look for an electrical problem, the first things you always check are the fuses and fusible links. On newer models it is a fuse in the under hood fuse box and on older models it's a fusible link.