Too f*cking hot

Starting to lose my sense of humour now. No.1 son has a bike - FZR250 (yes, I do know it's a Yamaha); ran fine on the test ride, but after the money changed hands it's overheating badly. I've changed the thermostat (remove fairings, airbox etc), and the fan temperature sender unit. Thermostat opens OK, fan ran in the shed, but on the open road the fan wouldn't go and the bike overheated. Shorting out the terminals made the fan run (blisters should heal soon - stupid frigging Japanese mechanics with hands the size of cats' paws!)...
OK, rant over... has the second temperature sender unit just shat itself as well? Why doesn't the fan work? Should I just fit a switch for the fan? Why am I paying for my son's bike? Actually, the last one's easy... Riding Partner!
OK, rant over... has the second temperature sender unit just shat itself as well? Why doesn't the fan work? Should I just fit a switch for the fan? Why am I paying for my son's bike? Actually, the last one's easy... Riding Partner!
