ive got the same prob......
the resistor is under the plastic cover.....beneath the wipers....under the bonnet
carefull not to crack the cover....very brittle....!
i found a temp fix......by chance....after much multi-metering and pissing about..
but..! im not leaving mine like this forever....
i wont go into all the readings etc.. but .....there is a 'overheating' bi-metallic strip..behind the resistors.. i drilled a hole in it and screwed the bugger down (in contact) that allowed me enough voltage to get the heater running...multi-speeds and all
but.....
it runs all the time the ignition is on..
i have taken the screw out for now to try to find the
real fault but if i ever get stuck...it
will be going back in...!!
highlighted the screw in the second pic...
the resistor is the big yellow thing..