When I pull the blade switch on my Craftsman 16.5 hp riding mower, nothing happens. I had this problem previously, and it was the PTO. Since that was a year ago, I really don't think it's that. Recently when the blades wouldn't engage, I checked/wiggled the wiring to the PTO, and the blades did engage. Does this indicate there's a problem with a switch somewhere? If so, where?

It certainly does sound like you have some loose connections in your PTO switch or even the harness. Get a friend to sit on the tractor so you can get a closer look at the wiring. Obviously you need to be very careful since the blades can come on at anytime, maybe even if you aren't touching anything, shorts can work both ways. Pull/push on individual wires with a pair of long nose pliers to see if you can isolate the loose wire. Your switch could also be bad, did you replace it last year to fix your problem?

I guess I should have given more details. I put a cement block on the seat (with the mower in neutral and the brake on! Lol) and pushed, pulled, checked the wiring into the PTO (the wiring into the blade activation switch has 10-12 different wires into it and cannot figure which are the PTO wires), and cleaned the contacts. Is there a way to check the PTO switch using a multimeter? Otherwise, not sure what I can check further. Am I correct in thinking the PTO switch IS the one that plugs into the PTO? May just have to see if I can order a switch...