Aprilaire 700M install help

I have an ecobee Premium and want to add my Aprilaire 700m humidifier to be controlled by the ecobee. I have only one extra gray wire that's not in use at my ecobee and air handler. Can I just take the brown wires, cap/wago them together with the gray wire, and use that?

Here is the manual with images to see what I'm talking about