http://www.ascycles.com/Illustrated_catalog/K100RT(2valve83-89)/catalog_frameset.html

Theres a diode on part 13 that lets current both ways !! Know its screwed anyone know what the board controls? thanks pete

Will get NEUTRAL LIGHT BACK!!lol

Your URL link is broken. Can you fix it? Otherwise we won'tknow what part #13 is.

I see that you are talking about the neutral light and I assume that you may have a problem on the instrument cluster.
There is a diode on the digital display.
When in neutral, the power going to the starter button comes from the gear digital display. If not in neutral, the power comes from the clutch switch.
The diode is to prevent the power to feed back the digital display when the starter button is feed by the clutch switch.

From repair experience:

80% - Transistor T10
15% - Transistor T9
5% - Diode.

Have a good look.

http://www.realoem.com/bmw/showparts.do?model=0504&mospid=47867&btnr=62_0234&hg=62&fg=05

Hi guys thanks rene,bert, have done the changes (following you and kerswell crank!)
The diode on that board is fine (current only goes one way). I have to pull clutch in to start though still.
The diode im on about is behind the clocks ( looking at faces) or directly upper left when flat in casing. Its shaped like a right hand bend , both or the connections are plugged in by the id call em pot rivets for now. That diode is totally shot both ways current .And still no nice green neutral, all other lights work. Tried using gear position switch thats been cleaned to see if if was just no connection still nothing. Only other thing was my transitor was BC174B replaced with BC547B ( tired but was one in discussion! ordered from cricklewood at same time).
Also gear display is just showing black splodge dot ( has done since i bought her and neutral was on then ) but i checked and found like little bits of rubber that go down on to board contact cleaned em (somewhere in past moisture obviously been in as a little limey).
Thought id get to it while i put alarm on and figured good electrical gods are with me day!
So confident when plugging back up then squat!
Plus side found rattle is alternator bearing giving me a warning!
thanks
pete