I have a Sears Craftsman 42" riding lawn tractor that has the electronic blade engage switch. The mower runs fine but when you engage the blades it runs for a few seconds and then shuts the mower down. I have bypassed the safety switch under the seat and also had to replace the clutch the pulls in the blades as the old one was bad. So what's the problem with this thing??

I think you missed another safety switch or the jumper is not good under the seat.

I would have to agree that the seat safety is usually the culprit when this happens. I guess it's possible that the ignition switch could be losing connection but that's grasping for a different answer.