Pangean
New member
I'm a new member and hoping that someone can help me troubleshoot a starting problem with my 1998 JD 770 compact tractor. The tractor started and ran fine approximately two weeks ago (its used primarily for cutting lawns and between the rows of a small, 5-acre vineyard). However, when I went to start it up a week ago: oil and battery lights come on when ignition key is moved to Run position, but the engine would not start. I suspected a faulty seat switch (plunger didn't seem to move smoothly) and replaced it, then also replaced the battery (it was getting a little long in the tooth and I decided to replace it regardless). I've also had the rear PTO and transmission neutral switches tested by the dealership - both fine. The battery connections and ground are clean and solid. With a person sitting on the seat (or the Seat Defeat switch activated), there is a loud click and the fuel solenoid activates. I can jump the starter and it works fine (tractor starts and runs smooth).
I found a wiring diagram for a 790 that seems to match up exactly with the 770 and an old thread on this site where JDGreen gave some detailed information/explanation of the starting and ignition operations (a big thank you to all those posters and contributors that have helped me get this far). Using a VM and light probe there is full voltage to the ignition switch 207 Wht/Red and all four outs when the key is turned on. However, there was no power at the end of the 105 Wht line to the Starter Solenoid. I suspected the K1 Start Relay and replaced it, but no change. I then exposed some of the wiring harnesses and on the harness near the parking brake mechanism I found two wires that had been chewed by a ? (mouse?). Both wires were chewed through. The other wires in the bundle were intact. I soldered a splice in the two wires and assumed that I had solved the problem, but still no luck. The chewed-through wires were Blu/Yel and Blu/Red so I assume they must be either wires connecting the S3 PTO Rear Switch and the S4 Transmission Neutral Switch to A1 Time Delay Control Module.
While I can jump the starter, there is a difference from its normal operation. Previously, the engine would start with the transmission in neutral and the rear PTO disengaged, even if the seat was not occupied or the seat switch was in the Defeat position. However, now the engine will only start when the seat is occupied or the seat switch is in Defeat position.
I guess my questions are:
1. Would the fact that the two wires (Blu/Yel and Blu/Red) were compromised have somehow fried the Time Delay Control Module?
2. What should my next step(s) be to troubleshoot the ignition system?
3. Based upon the fact pattern above, is there an obvious culprit / component that I haven't considered?
4. Have I overlooked something or, based upon the facts above, have I assumed that a component is working when it is not?
5. Should I eventually come across the critter that chewed the wires, is 12 gauge overkill??
Thanks in advance,
P.
I found a wiring diagram for a 790 that seems to match up exactly with the 770 and an old thread on this site where JDGreen gave some detailed information/explanation of the starting and ignition operations (a big thank you to all those posters and contributors that have helped me get this far). Using a VM and light probe there is full voltage to the ignition switch 207 Wht/Red and all four outs when the key is turned on. However, there was no power at the end of the 105 Wht line to the Starter Solenoid. I suspected the K1 Start Relay and replaced it, but no change. I then exposed some of the wiring harnesses and on the harness near the parking brake mechanism I found two wires that had been chewed by a ? (mouse?). Both wires were chewed through. The other wires in the bundle were intact. I soldered a splice in the two wires and assumed that I had solved the problem, but still no luck. The chewed-through wires were Blu/Yel and Blu/Red so I assume they must be either wires connecting the S3 PTO Rear Switch and the S4 Transmission Neutral Switch to A1 Time Delay Control Module.
While I can jump the starter, there is a difference from its normal operation. Previously, the engine would start with the transmission in neutral and the rear PTO disengaged, even if the seat was not occupied or the seat switch was in the Defeat position. However, now the engine will only start when the seat is occupied or the seat switch is in Defeat position.
I guess my questions are:
1. Would the fact that the two wires (Blu/Yel and Blu/Red) were compromised have somehow fried the Time Delay Control Module?
2. What should my next step(s) be to troubleshoot the ignition system?
3. Based upon the fact pattern above, is there an obvious culprit / component that I haven't considered?
4. Have I overlooked something or, based upon the facts above, have I assumed that a component is working when it is not?
5. Should I eventually come across the critter that chewed the wires, is 12 gauge overkill??
Thanks in advance,
P.
