I assume your running an automatic, if not don't worry about a neutral safety switch. That's just for automatics to keep you from starting the engine in drive or reverse and running over your family cat. Come to think of it, what a great excuse...
Two wires out of the heater should be two speeds. The heater probably grounds to the firewall. Run a hot wire to the orange wire, if the heater fires up the black must be for the other speed. If it doesn't then the black is a ground, ground it.
Are you having fun yet?
Also you can use a 14 ga link to protect a 10 ga wire. It will blow before it burns your 10 gauge circuit.
