[Speedy]

Yes, the main cable that goes to the S.Motor is the supply (+ve) from the starter relay.

Disconnect this, connect your +ve lead from your multimeter to it, and your negative lead to the engine/frame.

Push the starter button. You should see battery voltage.

(NB check battery voltage first, before any electical checks. Then you know what you should be getting. Any less, and it shows you have an issue!)

If you don't see battery voltage, bridge out the starter relay and check again.

If when bridged you see battery voltage, you can put money on the starter relay being faulty.

(On a curvy under RH side panel, Pointy, under the seat.)

Let me know how you get on.