Tractor Repair: John Deere 4100 gear Crank/No start, john deere dealer, john deere 4100

Question
Hello Arnie, I have a 1999/2000 John Deere 4100 gear tractor. Plowing snow on Sunday and it just died out. Found no power to fuel shut down solenoid. All fuses O.K. I hooked up a temporary battery hot to the white wire and with the wife cranking it over touched power to the red to engage the solenoid. Drove it back up to the house and got it in the garage. Is there some place to get a schematic for the start circuit. Could there be a safety switch gone bad? It cranks, just no power to the solenoid. I was thinking seat switch, but I talked myself right out of it as I have started it many times when I was standing next to it not in the seat. I am fairly mechanically inclined, I have tools and meters just not sure of the wiring from ignition to ???????? I am assuming that the key switch is the start of all battery power as there is only one wire from the starter connection, approx. 10 ga. going into a closed loom. I am assuming it must go to the ign. switch and power is distributed from there because without key on nothing works. I really don't want to start splitting loom and tracing wires if I can help it. Any ideas, suggestions or insight would be appreciated and welcome. Thanks for your time on this and all of the time you volunteer here.
Dan

Answer
Hello,

  Sorry, but I have no access to a wiring schematic as I don't work for a John Deere dealer.  If the operator's manual has no wiring diagram, you may have to ask a John Deere dealer if you can look at a schematic.  Shop manuals are pretty pricey.  It could be something as simple as a poor connection in a harness plug, or a loose wire on the back of the key switch, or a bad relay.  Or this could end up being more complicated than it sounds.  Wish I could give you a more definite answer, but that's impossible since there could be many different causes, and I haven't worked on one of these personally.  Tractors now have pretty sophisticated electronics and safety interlock systems.  A problem with the safety switches will normally prevent the engine from cranking over, however most of these types of machines have a feature that once the engine is running, it will shut off the engine if you get out of the seat without setting the parking brake or taking it out of gear, or if you engage the pto without being in the seat.  To make this feature work, they use the interlock switches on the controls, and a variety of relays, diodes, logic circuits, and electronic modules.  Since you have verified that the fuses are all good, you might check that there is power to all the fuses.  Also,there may be other fuses hidden in a different location than the rest of them.  Check the key switch and all wiring harness connectors for loose or corroded terminals, and see if the wiring has rubbed against something or a wire has come unplugged.  Don't forget to check the grounds also.  If there is a relay between the key switch and fuel solenoid, try swapping it with another relay if possible.

                   Good luck,

                       Arnie