Took my 90 XT600E out for a few miles yesterday, stopped to see a friend, got back on, fired her up and the Green Neutral Light stayed on So now I am in Neutral in every gear. Could it be that the switch just went tits up? Any ideas?

Try unpluging it from the wiring loom first to test, but id sounds like the switch.

Hope its nit like the DR's? when the screw falls out inside the engine.

Mezo.

It is just one wire on the switch, I took it off but the light was still the same. Does that sound right Mezo?

So its using the ground of the engine (like a negative) so know is the question is it normally closed or normally open switch.

Are you able to ground the wire in the loom to the bikes frame (earth if you will) with a small bit of wire & see if the light goes out, hope you understand what i mean? put a bit of wire or metal in the connector on the loom side not the switch & touch the other end of the wire to negative.

You should also be able to use a multimeter set on continuity & put one end in the connector going to the switch & again the other touching ground, try selecting a gear & neutral & see if the meter changes.

Mezo.

The switch is normally open, so if you ground the wire the light will come on. The problem on mine was the loop terminal on the end of the wire was large enough to touch the inner and outer parts of the switch so the circuit was always complete. Once I put a small looped connector on it was fine.

good luck