Alright, so I think I finally got it. Good enough for a first go at least. Here is the latest schematic. I cleaned it up a bit so it should be a little easier to read. I've also added a power switch for the mod. Power it down if you don't want it used and all operation returns to normal. I've also added a "engine off" LED to visually show you the engine is off.
So, I started working on mounting the sensors into the car.
Here is the LED mounted in the shifter housing.
Here is the photoresistor mounted inside the housing. I put a dab of epoxy on it to hold it in place.
With any luck I'll have the rest of the stuff soldered up on a board and into the car sometime this weekend.