I finally got some sun so I could work on this.
Well, the key switch has caused lots of problems so you might try squirting some WD40 or (even better) electrical contact cleaner in the key hole and then cycle the switch several times to see if that helps. Even if all other key functions are normal, the "crank" contacts could have a problem.
I Unplugged the ignition switch and confirmed that when in crank mode, there is continuity between the hot and crank connectors on the switch harness. Is this sufficient for showing the ignition switch is ok?
The start relay has caused problems for some folks. This relay is identical to the adjacent stop solenoid relay. You can try swapping connectors between these two relays as a way of testing the start relay. These are located on the "firewall" in front of the fuel tank.
I unplugged the 5p ignition relay (#1 in the manual & the left most relay on the engine wall when looking from the front).
I tested continuity according to the service manual:
Relay 30 & 87 - No continuity (ok per spec)
Relay 30 & 87a - Continuity (ok per spec)
Relay 85 & 86 - The spec says it should be 84 Ohms.
I am not exactly sure how to read my meter. Touching the meter's two leads together registers a 3 on the ohm scale
My meter has 10x 100x & 1000k settings.
On 10x, it reads about 17
On 100x and 1k, it reads 3 (same as no resistance)
Note: On the harness coming into the Ignition Relay, when ignition switch in cranking position, I have power to Relay 30 .
Before you get deeper into the control logic you can try a
brute-force starter test to verify the battery, cables, and starter are OK. There is a history of battery cable failures (under the insulation where it can't be seen) on some tractors.
At the starter, I jumped the (+ hot) across to where the small harness wire connects to the solenoid (?) metal tab. The engine cranked and started (which was great because I got to mow the weeds). So this should prove starter, battery and cables are ok.
On the HST model they don't use simple limit switches or relays to detect "safe" neutral or PTO setting. There is a box called the "cruise unit" that gets signals from the PTO and a rheostat on the shift lever and then provides a ground path for the start relay only when the safety conditions are satisfied. Do you get a good "neutral" light on the instrument panel when in neutral? If not, you may hae a rheostat or cruise unit problem.
The neutral light does come on solid with the power on
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LASTLY, at the starter, when I connect the meter's leads to the (+ hot) and to the little harness wire which goes to the starter (solenoid?), when the ignition switch is in cranking position, I barely register any power (the needle moves a little).
This seems to all tell me that I am getting power to the relay but the power is not making it to the starter (solenoid?), which would point to the ignition relay being bad.
Would you agree? Thanks for your reply.