So I read the manual and for some reason I still can’t understand what this plug is used for ? Can anyone help. 

Isn't that for using the built in transducer? You hook up an adapter to mate with whatever brand of depth finder you have.

16 minutes ago, Scott F said:

Isn't that for using the built in transducer? You hook up an adapter to mate with whatever brand of depth finder you have.

Ok I don’t think my current fish finder is compatible with that. It’s a basic hook 5 that came with the boat. 

1 minute ago, Ksam1234 said:

Ok I don’t think my current fish finder is compatible with that. It’s a basic hook 5 that came with the boat. 

It is compatible. Minn Kota sells the adapter cable that replaces the transducer cable for the Lowrance. Plug the adapter into the depth finder, and the the "spare" plug into the adapter and the built in transducer in the trolling motor is used instead of the transducer you might have mounted on the trolling motor.

9 minutes ago, Scott F said:

It is compatible. Minn Kota sells the adapter cable that replaces the transducer cable for the Lowrance. Plug the adapter into the depth finder, and the the "spare" plug into the adapter and the built in transducer in the trolling motor is used instead of the transducer you might have mounted on the trolling motor.

Well darn I had no idea.  Thank you 

Here is a list of adapter cables 

 

https://www.minnkotamotors.com/learn/technology/trolling-motors/universal-sonar-2

 

Make sure your Ultrex has the Universal Sonar transducer.  The have a new mega model that only works with Humminbird units.