I have a new Holland tc30 HST.Last year I overridden the seat safety switch.Now he sometimes acts like he’s connected.Engine runs but shuts down if shifted at any speed. The same when the emergency brake is released.Usually after a while it’s fine.After driving for a while it cuts out briefly.
Have you checked the seat bypass harness? Is it still good, and causing an intermittent problem?Is the seat harness OK? The seat and harness switch is the only thing that will kill the engine. You have to complete the driving circuit, and if it is not complete, does the tractor see it (like no one in the seat)?
The seat switch completes the ground circuit back to the key switch. The tractor has a delay relay, it could be a problem.