have you checked the fuses and relays ? I have twin turbo type fans on my S2 not sure if its standard or not. I think from memory these are 2x stage /speed fans so will probably have two sensors, 2x fuses and 2x relays .
wish I had a decent electrical schematic.
This excerpt from Clarkes site
Check the fan operation - there are two. There are two relays that affect fan operation. One controls the one fan during normal operation and another that controls the other fan when the A/C is on. Only one fan operates when the A/C is off, turning on the A/C activates the other fan. Neither fan is necessary for highway cooling (in fact, they get in the way) so you may only notice over heating in stop and go traffic. The fan switch in the radiator can fail with the fan off, or on. If the fans won't run under normal conditions (sitting in traffic while your temperature climbs) the switch is probably stuck off. If your fans continue to run long after you turn off the car, draining your battery, the switch is probably stuck in the on position. Many people have sent questions regarding problems with this thermofan switch, so I will explain here. The thermofan switch is a plug that screws into the radiator just below the inlet for the upper radiator hose. It has two wires attached to it. This switch monitors the temperature of the coolant in the radiator & decides when to turn on the fans. At one point, the normal cooling fan will kick in, and at the high temp point, it will turn on both fans. If your fans continue to run after shutting off the engine & drain the battery or do not come on at all, chances are the thermofan switch is bad. (There are more details on this below, in 7.6)
The coolant radiator has a temperature switch in it that controls the radiator fans. Even after the ignition is switched off (and the key removed), the fan will run if the coolant temperature is high enough. The objective is to keep the engine from "heating soaking," which can boil coolant in the head and block. The fan switch can fail in one of two ways. If it fails "closed," it will run the fans continually, which will drain your battery. If it fails "open," the engine can heat soak, coolant will boil and will push out the coolant reservoir's overflow hose. Coolant will also push out because of a failing head gasket. You can tell whether it's the head gasket or the fan switch by noticing when coolant is pushed. If it comes out the reservoir while driving, it's because of exhaust gases pushing through the head gasket. On the other hand, if coolant is pushed only after shutting down, it's the fan switch. To replace the fan switch, you'll need a 30 mm. deep socket, a new switch, and a new fibre sealing washer. The switch is different for early and late model cars. Be careful not to over-torque the new switch - you are threading it into a plastic radiator tank.
