[doug-5er]

(Quote)
How does the switch/spring engage that control slot?  Is it simply held down into the slot by the peg on the handle?

I see you removed the handle for clarity, that spring if you look at the underside of the handle should rotate with the handle,Make sure the bushing is on top of the round part of the spring that goes on the control shaft.The bushing is the same as the round part of the spring.When you put the tuning handle back on the shaft line the spring up with the center of the handle using a thin screwdriver or something thin to depress the spring as you slide the handle housing down on the shaft.If you need more help just ask,Like I said it's an SOB.But i wasn't going to let it beat me.That notch is just for clearance when the spring is depressed.