Have zippo familiarity with your brand, but to build on the above post....
If indeed you have a 3 wire, 2 coil solenoid, the symptom you describe might indicate both coils are staying active. A typical starting sequence has power to both coils for only a few seconds. Both coils are needed to move the solenoid piston/plunger to the open position, and then only one is needed to keep it in the open position.
So potential failure modes might be:
l
- Wiring is bad. Live short allowing both coils to remain active;
- “starting” coil and “running” coils leads reversed. ( wired incorrectly. Genuine or aftermarket part?)
- Another short somewhere between the starter relay and the solenoid allowing both coils to remain active.
- Something else causing inappropriate flow of voltage. Like whatever it it that causes your "start" to activate is stuck (see below)
If you can find a theory of operation and try to understand what causes your shut off solenoid to function correctly, that would help. The Deere’s I’m familiar with have circuity that controls the duration and timing of the fuel solenoid. As stated above, don’t have any idea about brand M. If you're handy with a multimeter, you could test the leads to the solenoid for 12 V. With the switch turned on, there should initially be 12v on both leads, then one lead should drop out. If Mah built the function into the start switch, the pull in voltage might only be present with the switch in the start position. Again, understanding theory of operation will narrow things down.
If/when you figure out which lead is the "start" and which is the "running" lead, you could bench test. Pull the offending solenoid then connect the live leads to a 12v battery one at a time. If it overheads with only the "running" lead energized, you'll know the solenoid is bad.
Why did you replace the old one? Is it still functional? If so you could check the ohm values of each lead and compare to the new one. That would provide a clue about possible coil shorting.