Got the car back and removed the bumper for access to rad coolant fan equipment. The fan does not run on test in the low speed selection. Today I disconnected the control wires plug and identified the low speed relay control relay connections to connections 85 and 86 on the relay. The car was not switched on but its battery was connected. I slaved in the two control wires to a separate battery and lo and behold the fan ran at low speed. So the problem lies in the control wires from the disconnect plug to, I assume, the ecu. With car power on I get battery voltage on one of the cables which feeds 86 on the relay. So the other cable is the return from 85. I checked the continuity of this as and was expecting it to be the earth but there was no continuity. Now I am assuming that this is the control circuit which means it is looking for an earth when the coolant temp reaches the low speed fan trigger point through the ecu. But during the fan tests the low speed fan does not test. I assume the ecu overrides the sensor and supplies the required signals to allow the fans to test. So from that I reckon the sensor is OK as it was replaced when I fitted the new thermostat module. So I assume the fault is either a wiring fault on that cable or the ecu. Any thoughts?