Engine won't run unless neutral light is on!

Just bought a R reg CB500 which has been laid up for a long time.
Cleaned carbs and plugs and starts well but every time I put it in gear it stops!
Tried bypassing clutch switch.
Side stand light goes out normally.
But the engine will only run when the neutral light is on!
Any ideas as what might be wrong?
Cheers
Alan

Stand stand switch faulty is my 1st thought.

Or perhaps an earthing problem with the neutral switch.  Follow the neutral wire to where it joins the frame and make sure it's making a good connection.

If the side stand light goes out but it still dies it sounds as though someone has been tinkering with the wiring or there is a bad connection somewhere! As sully says check all the earth points but also pop the headlight glass off and split/spray/reconnect all the connectors.

Stand- but you look like you have answered that