K9F wrote:

Ignition on and reverse selected if you have access to a multimeter check you have a full 12 volt supply at the centre contact of the filament. Then with no power and the ignition off and out of reverse check for resistance between the centre positive contact and earth (there should be open circuit indicated) and negative contact to earth (there should be 0 ohms). Better still do the same check from the positive to earth using an insulation tester and the results would indicate if you have an insulation breakdown between the switch and the holder.

Bought a nice new Gunson multimeter....just need the 2 week course to learn how to operate it!.
Shows 12.45 Volts for your first check...think i've done the next two bits and all seems ok.........as this is intermittent I am heading for the reverse switch on the gearbox as suggested by martinfiattech..........curious about getting to it as from initial rooting about underneath it seems well hidden!.......cubby box out and floor up the way forward?


Further to the above........rooted about and wiggled every wire I could find...replaced fuse and light on.......stood at rear admiring the bright glow and decided I'd had enough of electrics for today......shut the rear door.....light went out!....checked fuse......blown!.........any more suggestions folks?....not got a lot of hair to start with and all this head-scratching is not doing me any favours!