Okay so I've taken the plunge on the electrical stuff!
First off here's a diagram of the electrics with an FIA cut off switch:
Credit goes to Richard from http://www.visionracingdevelopments.co.uk/ for helping me out with this!
I'll be using the cut off switch to hijack the car's live feed as per MSA regulations. I'll also be using the starter switch panel in place of the ignition barrel, as the wiring for the ignition will run through the cut off switch anyway. The ignition barrel still makes a handy anti theft device because without the key the steering lock will be on!
The battery cables though the bulkhead:
A battery cable runs from the live battery terminal to the left cut off main terminal in the diagram. Another cable runs from the right switch terminal back through the bulkhead to join with everything that was connected to the battery. The hole though the bulkhead needs making a bit wider and rounder, so I can use a large rubber grommet to keep it tidier and more water proof I guess! Failing that I might try and source some sealant.
The main ignition feeds will have to go though 2L and 2R in the diagram as this has to be switched by the cut off - even if you disconnect the battery the car can still run as I accidently found out when jump starting it! Highly inadvisable though you'll fry your electrics after a while. As they are going through the cut off switch, they can also go through the starter switch. The starter wire will also go through the starter button.
1L and 1R are joined when the cut off switch is used and set to off. This essentially allows any current from the car, namely the alternator which is producing lots of current, to go somewhere i.e. to earth and the batter negative terminal, through a beefy resistor. Otherwise all that current would have to go somewhere and it would upset things!
In summary the 4 main wires in the ignition are:
1) Red (12 volts + straight from the battery)
2) Purple,
3) Green,
4) Black.
Purple and Green are the car's power systems, they'll be wired through the starter flip switch (this represents turning the key to step 1 and 2), the black wire will also be wired through the starter button (turning the key the final bit to start).
With the dash out it's been much easier to get the switches bolted properly in place.
The cut off switch is in the "on" position, I just have to route the external handle cable from beneath to pull down.
Getting somewhere!