Electrical intermittent can be tough to diagnose. Any remote starter or alarm systems? It could still be an intermittent starter solenoid. One way to test this is to get about 5 feet of speaker wire and solder and tape apart the leads of a 12 volt 'peanut' bulb to one end and insulated alligator clips to the other, like a giant test light. Attach one clip to the smaller starter solenoid Brown wire (T40 in diagram) at the starter and the other clip to ground. It won't matter about which side goes where, polarity isn't important. The large starter wire should have power all the time.
You can place the bulb within view of the driver by gently closing the hood on the wires in a spot where they won't be pinched and cut by a sharp metal edge, like against the rubber strip that runs along the rear of the hood. It will just blow a fuse if it happens to short (carry an extra 40 amp maxifuse if you want or just swap it with a rear blower or some other adjacent non-critical maxifuse to get you home).
Laying it on the plastic cowl screen will ensure that any exposed leads won't short to ground. Tucking it under a wiper blade may be OK if it won't rain or you don't plan to use the washers, but it is easy top forget that the bulb is there, so I won't recommend it.
The bulb should light everytime the starter works. If it still lights and the starter doesn't work, the problem is in the starter. If the starter doesn't work and the light doesn't light, then the problem is upstream towards the starter relay or IPM. The PCM can also prevent cranking if it doesn't see Park or Neutral.
If you suspect the ign switch, just move your test light inside and clip one end to the Yellow start wire (A41 in diagram) from the switch and the other clip to ground. Move the wiring out of the way of your feet and pedals and place the bulb where you can observe it during cranking. You will want it to act up in order to diagnose it.
Circuit here:
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