The ECU (engine) light comes on and stays on until the engine starts, then it goes out. Just to verify what I was thinking, I just turned the key on mine with the switch in the run position without pushing the start button...the ecu light stays on....... until it's started.
Did the ecu light come on prior to stopping the engine at the petrol station or did you only notice the light afterwards?
The ECU light has nothing to do with the starter relay I'm fairly certain.
If the light came on prior to stopping the engine, that would point to other issues....which I doubt.
Try the jumping of the solenoid terminals, and if it cranks, then either your not getting voltage to the solenoid from the start button...most likely corroded terminals, or the solenoid is bad (the contacts that take power from the start button) . You could open up the handlebar switch housing and have a peek also....spray a little electrical contact cleaner on the button contacts.
Keep us posted...there are plenty here to offer help.