My John Deere L108 mower will not crank by the ignition key alone. It doesn't even make any noise. However, it will crank as soon as I put the jumper cables to it. It will run fine for hours and then do the same thing every time that the power is killed via key or emergency stop (no weight on the seat). I have changed the battery out with a new one last summer and this didn't change anything. Could it be the ignition switch, ignition module, or something else? How do I verify the operation of these items?

Hi,
To mechanical devices in the start circuit; one is the switch and the other is the solenoid. Both are common failure points. A way to check to see which one it might be is to turn the switch to "on" and touch the jumper cable to the non-black small wire on the small post (tabbed) of the solenoid; if it clicks and starts, then it is the switch.
Be aware that it is not all that unusual to have them both fail; especially if the mower is commonly at rest in the weather.
Peace,
Clarke