My NH TC30 is running again. But I am still puzzled by the cause or condition. When I installed the new start safety switch the tractor started and ran. But when I engaged the trans the engine stalled. I tried a couple of more times and it would start but stall when I tried to engage the trans. Taking a quick look I discovered I had failed to reconnect the seat switch. So I reconnected the seat switch, tractor started and everything worked fine and I used it for a couple of days with no problems so I assumed the start safety switch had resolved the problem.
Then I parked it for a couple of days and the condition returned and I was back to square one.
Today I decided to start with the safety switches again. I inspected them to see what kind of terminals they use. When I got to the seat I remembered how it was disconnected when I installed start safety switch. Out of curiosity I disconnected it, and low and behold the tractor started and like before stall when the trans was engaged. I reconnected the seat switch and have started it several times and for now everything works.
Needless to say I am stumped as to what is going on or what to do next. For now I will just have to monitor and see what happens.