[wilkin250r]

That's pretty close to how I would have done it, but it might be easier to replace the pair of relays with a single DPDT relay.

In any situation, you're running an additional wire to the valve. Whether you change the switch on the dashboard to the style designed specifically for the motorized valve, or you run relays under the dashboard and run power, you're STILL running an additional wire, you can't do it with just the single wire.




On a side note, just because it's an interesting project, I think I've found a way to run the motorized valve with just a single wire, but it would involve a power module (about $20) and a relay, not too much different than a pair of relays.