This is the iron-wired feedback diode which rusts and cracks leading to no fan speed except on "High" or "Demist"
A touch with a screwdriver and this happens
The power transistor which allows variable speed fan running. They soemtimes fail short circuit in which case the fan runs all the time even with ignition off
New power transistor
Backside of the pcb. Excess (brown) resin is from the factory....
We lacquer the boards after repair to help stop them getting damp
How the controller is fitted
... Like this!
The controller sits in the airstream from the fan as a cooling technique, but it means the components are subject to continuous moist airflow