Safety Switch Issue?

I was just given a 1995 craftsman Lawn Tractor, 46" mower, 6-speed transaxle, Model #917.272010, with a Kohler 16.5HP engine. The engine operates strong and smooth. However, when I let off of the brake pedal the engine shuts off just like I had turned off the ignition switch. Also, if I pull out the mower deck switch to turn on the blades, the engine will cut off. I was told that it worked fine until it was parked 1-1/2 years ago when the owner purchased a new mower. I've been told to bypass the seat safety switch, which I did, but that did not change the issue. I see in the manual that there is a "operator presence relay" and an "interlock switch". Has anyone seen or heard of a fix for this issue? Any insight would be appreciated. Thanks! Cody