When my UK Amazon was converted to OD, the switch was fitted on the far end just above the windscreen wiper. Not standard, but it seems to be easier to find. A 1960s review from Autocar(?) queries the red colour since this is traditionally a danger colour, but at least you can see it clearly. Also for years I was driving with the switch the wrong way round, i.e. flick up to turn on; always annoyed me since the most urgent movement you make is usually to turn it off, and this goes with an ergonomically-easier upward movement of the hand.

Tom