It does sound like the seat switch or possibly the connector. A basic ohmmeter can tell you if the switch is working. Some feature a tamper proof connector that has a little spring that shorts across the 2 terminals should the connector be unplugged and on occasion they fail.

I was referring to the connector at the seat switch. I'm not sure if all of the YTH1542Xp tractors are the same. the product number or if you have the proper part number for the seat switch in your manual that could help. On some versions of the 2 wire connector at the seat switch, there was a spring and a small plastic fulcrum on the inside of the connector. This was on the switches that opened the circuit when the operator was present. That way, if the connector was pulled off the safety system wouldn't sense the operator presents and you could not let your foot off the brake nor engage the PTO. If yours does not have that version and there is no visible damage, a new seat switch is a cheap and easy thing to try. I'm not aware of a 4 pole switch that has this feature. You could still have other items that could cause this, but the seat switch is a likely cause. Maybe it is as simple as another operator adjusted the seat too far rearward for the switch to be able to sense that you are there!

You wrote: Thank you for your reply to my post. Could you give me any idea as to where to look for the connector that you mentioned in your reply. I need to check about the spring and need to see if the connector is the problem; however I'm not sure where to look. I have the user's manual, but can't find anything that sounds like sensing switch or safety connector.