Sorry if this is a dumb question:
Where is the switch for the rear wiper & the heating element on a 1990 defender 110.

Also there are a few switches on the RHS dash, one is the hazard, the second is the cabin light, the third(???????) there is a small white knob on the RHS steering console? Dont have a freaking clue what it is?
Some help will be appreciated.

Rear wiper? Heated rear window? Probably never had one I know mine hasn't.

On my 86 90 the third switch net to the hazard lights is for the heated window.

The rear wiper is the other side of the clock from the lighter.

The white knob on the RHS sounds like it has been put there by somebody to do something - this hole is usualy blanked off on a diesel as it is where the choke cable/knob would be on a petrol - its a very good place however to fit a switch if you need one!

If you take it out you will need the rubber bung to blank it off - difficult to find me thinks