If you unplug the power - remove the balls (important) and lift the playfield. If you move the flipper bat by hand - when it reaches the end of its travel (ie end of stroke) on the underside of the flipper you should see the crank arm either open the switch or close the switch...I can't remember if they are normally open or closed!
Hope this makes sense.
http://www.pinrepair.com/wpc/index3.htm#flipSome better reading re flippers.
