I drove the Zetec for the first time in about a year today (long story), and I found the radiator fan would not trip. Fuse good. I jumped the fan to ground, and it spins just fine. Non-Focus setup, with radiator from PMA, U.K. I tested the thermostat on the stove-top, and it tripped w/in about five degrees Fahrenheit of target. I took the water hotter, and resistance hovered between .8 and .9 all the way to boiling.

Would that level of resistance stop juice to the fan? Clamp connections were solid and tested to '0.0'. I don't see any other players in the circuit that could cause a problem. Fluid system was bled, and I could visually see fluid in the radiator covering the level of the thermostat.

How is the connection bridged inside the thermostat? From the outside, the system appears pretty fail-safe.