This is what I did for the zx-9r.net site, so remember this is for the zx-9r, and on the zx12B3 onwards there is a diode in the system that does away with one of the switch wire lines.
Clutch switch checking, cleaning and/or replacing, with pictures. 8) Pt No 27010-1094 Make sure bike is out of gear before you start
This will help sort out, Bike won't start with the clutch in, Engine only starts in neutral with the clutch out, the bike only starts with the clutch held in, and other variations, and some intermittent neutral lights.
If the engine does not turn over with the shorting link fitted as shown it the pictures, then it's not the clutch switch, but clean it anyway.
Tools 5mm Allen driver or key
Large instrument screwdriver or small screwdriver
Scotch Brite or similar, see the last picture.
Coat the contacts in Vaseline after cleaning to help stop future corrosion.
Now put the bike back together.