DV,
Ok if I've done this correctly a schematic will appear below this line.
This is just the general idea. It could be made significantly more complex. In this simple one the first toggle switch (leftmost) must be off. The second and third toggles must be on. The fourth toggle off. And then the starter button depressed. Note that I've used only half of a dpdt toggle. The other half of the toggle could be used for controlling other electrical items.
If you wanted to get very fancy, you could make all of the toggle switches in the car part of the combination lock as long as the engine wasn't running. Then, after the engine was running, the toggle switches would revert to their normal function (you'd want to flip all of the toggles off after getting the car started). This fancy method would require relays at each toggle and a simple circuit to measure the rpm of the engine (fundamentally a simple integrator circuit made up of a transistor, a couple of resistors, and a capacitor). Obviously out of scope for a simple reply here on the forum
I did have a thought of using the high beam button on the steering column stalk as the starter button ... but the impulse passed
Back to the simple circuit... of course you'd want to lable the switches to confuse folks. Name the first switch "fuel pump" (since it has to be off for the car to start), the second "
oil heater", the third "brake lights", and the last one "ignition module".
Hope all of this helps...