Their should be pulleys in the front of the tractor that slide in and out when you push on the rod (on left hand side of tractor at your foot)...push rod=mower engage, pull=mower disengaged...Key switch is a matter of wiring bugs..go to sears website, and go to the parts department, and look up your model #...You can get a wiring diaghram..

Actually, there is a picture of a tractor with this part at the top of the page. You should be able to buy one easily enough. Search "sears suburban" on ebay and look for a part called a mule drive. (What you're missing)