A couple of things I noticed. First I'm going to assume your use of the word "open" above means "to enable" or "send power to", as an electrician of sorts that confused me, but easy enough to overcome.
Here are the rest of my observations:
Are you using magnetic or contact switches on the shift mechanism to determine neutral? I did that once, it worked out well for me, I used magnetic switches.
I'm concerned about your use of "ACC", if you try to start the car (power to starter) with the key in ACC (i.e. that yellow/black wire on the ignition switch has power, thus powering the load reduction relay (HVAC, lighting, etc) the car wont run. There is a seperate position in the switch that powers the big black wire, which is "RUN". that wire needs power in order to run due to turning the starter. And dont forget about the red-wired "key in ignition" contact switch in the ignition switch that powers things like the radio and the instrument cluster.
I'd also trace that red/black wire, or meter it to see if it doesn't already give a neutral safety signal you can use.