Hi grumpy, that device with the spring is a Bowden cable operated on/off switch...ie. squeeze the handle (or whatever procedure) pulls the centre (of what looks like a solenoid) and makes contact and motor runs...let it go and the spring pushes the centre collar back....motor stops.
If you look at the very first pics posted, you can see the cable enter the box, with adjustment similar to that of the Model 45 roller clutch. wink

Please do not PM me asking for support. Please post your questions in the appropriate forums, as the replies it may receive may help all members, not just the individual member.
Kindest Regards, Darryl grin