Sound to me as if one of the safety switches is not operating properly whether the switch is bad, out of adjustment or a broken wire. Use the trouble light or multimeter to trace the bad switch or wire
Here is the ariens site for the manuals for your machine. I tried to attach the parts book were the wiring diagram is in but file was "too big" and being to computer illiterate to figure out how to just copy and paste the wiring diagram --- So here it all is. Don't know if the wiring is different per serial number just be sure to use the right one.
Hope this helps
If you misplaced your Ariens lawn mower or snow blower manual, You can download a copy here.
www.ariens.com