94 xj6 cooling fan operation

I have a 94 xj6 with the dual electric fans, I have had some overheating issues and the fan does not kick on. I removed plug from switch on radiator and bridged the two outer prongs and the fans come on. What I want to know is what the third prong does and if there are multiple speeds.

Nicola - Technical Service Bulletin.86-140 ( available here: JagRepair.com - Jaguar Repair Information Resource ) addresses inoperative fans and may be of help. I will also attempt to send you via PM a wiring diagram for the fans circuit.