I have the 7 prong transducer cable coming from the 360 Imaging transducer AND I have a 7 prong transducer cable coming from my Helix unit. I believe both are to plug into the back of the Helix but it only has one 7 prong transducer connection point.  

 

So I called Humminbird support a couple weeks ago and it was recommended to me to purchase a Mega 360 7-pin Transducer Y-Cable so it would all connect together - BUT I’m not seeing how it would work. I was envisioning more of a splitter that would allow both transducer cables to snap into the back of the Helix. 
 

Anyone figured this out before? 

find your combo and it should list the connectors needed.
 

https://humminbird.johnsonoutdoors.com/us/support/networking-diagrams

I have Mega 360 connected to by Solix up front along with the  transducer built into my Ultrex.   I used the cable they recommended.  It’s a y cable.  You connect one end to the fish finder and the other end of the y has two cables to connect to 360 and your regular transducer.   It’s very simple and there’s no way to mess it up that I can think of as long as you get the right y-cable.

I got a call from somebody from back home that wires boats and I think he got me figured out.  Hope so!!