Just realised that my OE airbox was missing both some plastic spiral wiring protection and a rubber throttle cable guide/restraint at the front of the lower part underneath the snorkel - the lack of this rubber allows the throttle cables to move when the bars are turned and it was this movement that wore out the adjacent wiring insulation which then burnt out - a difficult problem to both find and to fix.

If you have the OE airbox or at least the lower part only, as I do, suggest that you check that you have the wiring protection and the rubber guide - for those that don't have the OE airbox, ditto re the wiring protection and/or find a way of stopping the throttle cables moving laterally.