Willandrip
Please accept my apology for asking the question again, when I asked ther original question I read your reply when I was abroad and thought I would digest the contents when megabits were cheaper back in the UK. I then forgot I had asked the question as I got involved in loads of other issues relating to the carbs. Anyway your explanation is perfect and thanks for having the patients to reply again.

Cheers

Keep the reserve switch; it is a useful item if operating correctly.
N.B
The electrical reserve system on YAMAHA motorcycles will revert to "reserve tank on " position by default if any component in the system fails or is disconnected.!!!!!

To test the system with the 5v LED mod simply;
leave main tank on,
run tank till you expect reserve LED to show =120 miles from full approx.
LED should flicker/glow/illuminate
Keep going another 3 -4 miles
Bike should emulate fuel starvation
Switch to reserve.
Bike should pick up it's skirts and head off into the sunset/moonlight.
Refill as available=LED will go out.
If not inspect system for breaks in sensor wiring (solder joints brittlefy (is that a proper word ???) due to contact with fuel/vibration.
Inspect rocker switch=water gets into a rarely used/tested switch and verdegris bulds up=judicious use of electrical cleaning fluid c/w manipulation usually cures.!
A wise man replaces with an illuminated switch if unservicable.
This is of particular references to the larger machines =
You DO NOT want to be faffing about with out of reach switches at 130mph+ in the dark