Ours did not come with the plug either.  We had to order it (AG427254) through our dealer.  As bobby greif described, it has 2 hand screws at the edges to hold it in, and can be wired to the spray controller.  Even without the plug, pressing the red screen arrow to toggle on and off beats getting out to mark the spot, just takes a little more effort than having it toggle automatically by the spray control.

MO1466, to configure the cruizer, go into the "system" menu and select the blue box labeled "switch".  There you can select between screen toggle or hardware toggle, I think the plug has to be installed before the hardware option is given.