Toro Proline blades disengage

I just purchased a Toro Proline 48 (Model 30180) with a Kohler 16 Magnum (model MV16s). I believe it is a 1995. I purchased because I have a good pitch to my lawn and was tired of using a 21 inch mower. The mower runs great when going down the hill but as soon as I turn and it start to go up the hill the blades disengage. They shut down and only come back on when i turn around or get to a flat part of the lawn. I was looking for a loose wire but did not find anything. Was wondering if it was some kind on safety or if it is electrical. I can also get it to disengage when I tip the mower back. Any help appreciated. Thanks in advance!