I have a Rally, made for Craftsman, model 18544B, 18.5 HP Briggs, 42 inch cut. I am told it was made byAYP. Blades have stopped engaging. I have replaced the PTO switch. Following the wires some lead to a plug in into the mower that is in the base of the frame on the right side, just above the deck. It is square and pronged and plugs in to something attached to the frame but there is only the plug in-it is not attached to other wires. Am I missing something? Is this part of the engagement process? Seems like the other end needs to go somewhere unless this is some kind of contact to engage the blades and it maybe isn't working.

Wires should be running to the safety switch. And they will only plug in to one end, the other end is a plunger that is round and is activated as the blades are being engaged.