have you checked that there is a 12 volt feed to motor when fan is switched on-check on all motor speeds.if not then it may be the heater resistor unit at fault.also check that the heater fuse holder blade is live at one side with fuse taken out, and heater switched on.if there is no live feed on any of the heater fuse blades [with fuse out]then the fuse box will be at fault.it may be a broken joint where blade is soldered on printed circuit board! you may need to run a new fused ignition fed supply to rectify it or replace fusebox .or if you are able you could strip fusebox and re-solder joint!!
k, November 2015
