John Deere L120. When the mower clutch is engaged (switch pulled outward), the engine dies. Appears to be safety interlock related because the engine will recover if the PTO switch is returned to off.

t sounds like there may be an issue with the safety switches on your John Deere Z225 lawn mower. These safety switches are designed to prevent the engine from running if certain conditions are not met, such as if the parking brake is not engaged, the arms are not in the proper position, or the PTO is engaged.
Here are some things you can check:

1. Check the parking brake switch to ensure that it is properly engaged. If the switch is faulty, it may not be registering that the parking brake is engaged and will cause the engine to die when you disengage the parking brake.
2. Check the arm switches to make sure they are properly positioned. If the switches are faulty or out of position, they can cause the engine to die when you move the arms.
3. Check the PTO switch to ensure that it is properly engaged. If the switch is faulty, it may not be registering that the PTO is engaged and will cause the engine to die when you engage the PTO.
4. Check the wiring and connections for all the safety switches. Make sure they are not damaged or loose, as this can also cause the engine to die.

If you have checked all the safety switches and wiring and everything appears to be in working order, there may be a deeper electrical issue with the mower that will require further diagnosis

The electric clutch draws current while engaged. It is quite hungry on power which means that if the battery is low, the generator may not be making enough to charge the battery and hold the clutch in too. This is why the batteries on these machines are so large relative to say an ATV battery. I have several times experienced units with low batteries which started the engine OK but would not hold the clutch in. The battery may be getting old and not holding the charge. Try charging with a mains operated charger. Make sure to check water level in battery cells. Running them dry can ruin the battery.

Most of these mowers have a safety switch between the PTO switch and clutch. A safety switch or relay is most likely the problem. Hope this will help ya.

check the fuse if ok check the safety switches

Most likely the seat safety switch is malfunctioning.

could be safety switches faulty or sticking,usally 1 under seat, and 1 by the catcher, pto toggle switch maybe faulty, if battery is low there won't be enough power for the clutch to engage. I would jump the clutch to make sure that hasn't died first cause that is the costly part.

You have several safety switches on your unit. The engine should not start if the PTO safety interlock is engaged. Be sure PTO switch is off.
If the sarter Does Not Work Or Will Not Turn Engine Brake pedal is not depressed.
or the PTO is engaged.
Battery terminals are corroded. or Fusible Link in starting circuit is blown - (Not likely unless bad wires) Here is a link to your wiring diagram (maybe your model)

http://www.postimage.org/image.php?v=Pq1tOfiS
Notice how the starting circuit goes through the brake pedal (must be depressed) and the PTO switch (must be disengaged) and that the PTO only works with operator present. Print that page while link still works.

The seat switch is doing it's job,you can;t get off the seat unless the pta is off and the tractor has the park brake engaged.Replacing the switch won't change anything.

Try a new seat switch,or the rio switch on the right rear of the trans-axle.

sounds like the seat switch is bad