SR961s solar water heater eBus info?

[jlgtx]

I have an SR961s solar water heater system (https://www.dudadiesel.com/choose_item.php?id=SR961s), that I am trying to connect to one of Reinhart's RPi eBus adapter boards. If I can get it talking, I can start thinking about the message formatting...but my first problem is that the eBus connection on this controller is three wires. 

Can anyone give me their best guess on which two I should be using?

[jlgtx]

Well, I heard back from the vendor:

"An eBus will not  work with the controller and  attempting to connect one could damage the product and void the warranty. I am sorry for the inconvenience. The manufacturer stated to me that only they can use the eBus connections and that a customer can not connect his own to it."

This, of course, begs the question why they'd label it "eBus" if it isn't eBus at all. It does help explain why I can't seem to get any comm signals out of it, regardless of which wires I use.