MG California stone will not start

Current on the lead going to the starter motor has a current but when placed on the starter motor the motor does not start. However if you short the two terminals on the started the starter works and stats the bike. Can ayone suggest what is happening

There’s usually a relay involved. That might be worth a look.

I’m not familiar with the wiring of a cali stone, but such symptoms are usually down to the all to common “click no crank” problem that afflicts many Guzzi’s.
Basically you need to runa new feed wire from the battery, then preferably through a fuse, to the power feed into the starter relay. On my Cali 3 that is located under the left side panel. the problem is caused by the original power feed going through several connectors and the ignition switch. chances are all of these have slightly corroded and cause resistance and there’s not enough power left to activate the starter motor.
Other poosibles are the cut out swithes Clutch, side stand etc.
Have a look at this video Moto Guzzi Click, No Start Fix - Starter Relay Bypass - 2004 Moto Guzzi Breva 750 - YouTube

I don’t know specifically about this issue on bikes, but it was common on old trucks and was the starter solenoid had failed. We used to put a heavy spanner across the terminals to start them until it got fixed.