Need some help to sort out a heater fan problem please.

The heater fan on my right hand drive 1992 Mi16 (1905cc) has stopped working. Can turn the rotary dial but no fan. Heater fuse is OK. Interesting the light on the aircon button goes out as the rotary fan dial is twisted! Wondering whether a wire has come loose or a bad earth?

Where do I start looking to resolve this problem?

Thanks in advance!

UPDATE:

Located the fan assembly under the glovebox. Removed 4-wire plug (presumably power, earth et al). Noticed aircon button indicator light no longer dims when I turn the heater fan rotary dial. Reconnected the 4-wire plug and previous dimming symptom returned. Suspect heater fan motor?

Removed the heater fan assembly. Fan turbine and motor armature turns freely. Applied 12V directly to motor and it immediately spun 100%.

So, fan motor not the problem.
But could it be the electronic circuitry on the heater motor assembly?
Or a bad earth or loose wire elsewhere?

Where should I look next please?

Thanks in advance!

It could well be the electrical gubbins that are mounted on the fan, the rheostat or whatever it is. They seem to be a common problem. Not cheap new, though they do turn up on eBay.

Thanks for this - a couple of other contacts of mine suggested the same thing, so I'm going to replace the heater fan control module (mounted within the heater fan assembly) first.

Check the reley where clutch pedal is.....
It should be yellow reley and this common thing .....