I'm a different person (Tom), but I've been having the same problem, so I'd like to join this discussion.
This was put together by a few forum members and might help. Let us know how you are doing.
First, check the fuse(s), check battery connections for corrosion (clean if necessary) and *voltage - above 12.5 volts should be good.*
Battery is OK. Starter switch and circuit breaker have been replaced. Push-on connectors at ends of cables to circuit breaker and solenoid have been replaced with ring connectors.
Second, check for power from the battery to one of the large terminals on the solenoid. ...
OK.
Third, *check for power at the small terminal of the solenoid while depressing the clutch/brake pedal and holding the key in the start position (you may need an assistant to sit in the seat to override the safety switch). If your solenoid is a four wire solenoid, check both small wire terminals as one is ground and the other is power from the ignition switch. *If your solenoid is a three wire solenoid, make sure the solenoid body is not corroded where it bolts to the chassis of the mower as this is your ground path back to the battery. *If in doubt, remove the solenoid and clean the mounting area down to bare metal. *If there is no power to the small terminal then your problem is most likely a safety switch, ignition switch or in the wiring.*
=> I get no power at this terminal (test point 10, purple wire from transmission neutral-start switch). Original solenoid was replaced some years ago, and new solenoid is a 4-terminal model. Other small terminal is well grounded.<=
Fourth, check for power on the other large terminal of the solenoid while holding the key in the start position (you may need an assistant to sit in the seat to override the safety switch).*
=> I get no power at this terminal (test point 3, cable going to starter motor. <=
Fifth, check for power at the starter while holding the key in the start position (assistant again).*
Starter was replaced some years ago and will crank if I connect a positive jumper cable to its positive terminal.
Sixth, check your ground circuit back to the battery.
OK.
I have the John Deere Technical Manual TM1206 (May 1985) for my tractor. I followed all the tests on page 42-05-5. Everything tests OK up to the test "Test Transmission Neutral-Start Switch Lead". The problem is, I have no idea how to find this switch. There is a description on page 42-10-15 "Transmission neutral-start switch is located on top of transaxle in font of sheave. Access can be gained by reaching in over frame by right rear wheel." I have looked in there and just can't see anything. Even if I could, I can't imagine how I'd get my hand in there. And even if I could get my hand in there I can't imagine being able to test anything. I also tried removing the mower deck and looking at it from beneath, but couldn't see anything.
I have a few questions for any experts that might read this:
1. How likely is it that the problem really is the neutral-start switch? I don't want to go to a lot of work and then find out that that was not the problem.
2. Are there any other problems that could cause the same behavior that are easy to test?
3. Is it possible to bypass this safety switch and forgo this safety feature? This tractor is over thirty years old and has a number of idiosyncrasies, which of course any old tractor is entitled to. It's never going to be perfect. I have looked at the wiring diagram on page 42-05-4, and it looks to me as if I could bypass the neutral-start switch by shunting the purple wire from the ignition switch (test point 3) directly to the small terminal on the solenoid (test point 10). The problem is, I don't know whether the neutral-start switch is normally open or normally closed, so maybe bypassing the switch wouldn't accomplish anything, or would cause a short circuit, or something like that. I would appreciate any feedback about the possibility and advisability of bypassing this switch.
4. If I really have to test, and possibly replace, the neutral-start switch, can anyone test me how to do this, and possibly send pictures or a diagram?
Thanks in advance for any help.