I'm going to give you one piece of lengthy advice - having dealt with a LOT of electrical troubleshooting in my past - one. thing. at. a. time.
DO NOT DEVIATE FROM THIS. DO NOT GET SIDE-TRACKED. DO NOT GIVE UP ON EACH CIRCUIT UNTIL YOU'VE FULLY TRACED THE ENTIRE THING.
That said there is a troubleshooting chart (page Z16) and a wiring diagram (page Z20) in the manual. The troubleshooting chart is pretty basic, but it's still good info. Use the wiring diagram to trace the power through the entire circuit. You can start from the beginning of that circuit or the end, but either way, stay on that circuit until you've eliminated the circuit as the culprit.
It is always the simplest thing that ends up being the problem - and almost always the last thing you'll find in your search.
You've got several ideas you've been sharing with us here, but we're not there with you. We can spitball ideas all week for you but you'll have to pick the most likely candidate and stick to it until you've either eliminated it, or found it. See the pattern?
I'm not at all trying to be a jerk - I'm trying to save you some time, so please read it in that tone. IMO, it sounds electrical to me and there are some good pointers provided here (e.g. starter inhibit switch).
Best of luck and keep us updated.