so then the wire you have hooked to the light switch should be re-routed to the ignition. that way when you turn the key to start it tries to start the engine.
Your on the right track, its just going to take some time to pinpoint each and every connection on its own. unfortunately you said its not a stock setup, therefore no one has a diagram to help. At that point, its trial and error.
Try something, LABEL THE WIRE!
Try something else, LABEL THAT WIRE!
And so on until you have something to go off from.