Well, my thermistor is on a 4300. First one was replaced under warranttee, but from then on I was on my own.
The fuel solenoid coil is NOT 12 volt but they feed 12v thru the thermister to make it pull in. After a few seconds the thermister cuts itself out of the circuit and hopefully the engine has already started with the solenoid held in by reduced voltage. Oh, this circuit seems to be a negative switched system as well.
I found that the solenoid is constantly fed (when the key is on) with 12 volt and the thermister is between the solenoid and ground.(white wire?) The third wire runs back thru another system that limits the voltage for normal running.
The next time my thermister quit (I am an hour from the dealer) I jumpered the white wire to ground when starting and the solenoid snapped in, Since the problem was intermittent I only had to do this on the first start of the day on cold mornings, most times.... Then one winters day my jumper wire shorted out while the engine was running and the smoke escaped from the solenoid..
The next two weeks I ran with the solenoid removed and a threaded rod that I had to screw in or out to start or stop fuel flow.
When I installed the new solenoid (they cost more in Canada) I used solder and heat shrink to do a neater job on the jumper, and last fall (the problem gets worse in cold weather) I hooked it to an "emergency start" switch that I touch if the tractor doesn't fire within three seconds. Works great.
I was also thinking of building a circuit that would allow full voltage to the solenoid when the starter is engaged....
The tractor now has about 6000 hours on it and gets plugged in when the temp drops below freezing.
