OK. I will give a brief outline now, and try and get a detailed drawing together.
The 40x2 handles most of the work. 4 bit comms with the Oled display etc. The 08m2 purely monitors the HC-06 bluetooth receiver and lets the 40x2 know via serial if a valid command has been received. I found having the 40x2 monitor the bluetooth slowed it down too much.
All 2 slots are full to the brim, and the other 2 are half full. In fact, I spent a good few evening clearing up the code to make space to finish it.
Tip122 transistors switch a signal to the 40A relays in the engine bay (purely because I had them lying around).
Pretty much it really. Mainly outputs to operate relays with inputs for the 'Enter' and 'Select' buttons, headlight full beam signal, reverse signal and ignition signal.
Voltage is monitored off the ignition source.