Thanks for confirming that. My solenoid does not have this button, but it is definitely faulty. I shorted across the main terminals and the engine now cranks but does not run. It turns over very slowly and the battery is struggling to hold the voltage up. I am now charging the battery.
I will order a new solenoid, and clean up all the terminals. The water pump over the top of the alternator and this solenoid is not a great layout!
SV Stella A54-154