Define "hook to my fish finder"?
Do you want to be able to utilize your fish finder (Lowrance) to follow a path, hit way points, move the trolling motor left and right, speed up, slow down, and follow contours? If so, you are looking for a Motor Guide XI5. Minn Kota doesn't offer the ability to do this sort of thing with a Lowrance unit as they are married to Hummingbird. If this is what you are looking for, you would need the XI5 motor and the NMEA 2000 compliant connections. They sell a kit that includes the power connection to the NMEA backbone, two terminators (on on each end of the buss), three "T" connectors, and pictails running from the "T" to the trolling motor and fish finder.
If you are simply looking to "hook your fish finder" (Lowrance) up to the trolling motor to utilize the built in transducer (US2 transducer on a Minn Kota) then you need the conversion cable that connects from the Minn Kota wiring (Small barrel connection) to the transducer port on the back of your Lowrance.
For me, I troll 95% of the time. I own Lowrance products but I do NOT own Motor Guide products. Do I wish that Minn Kota would allow Lowrance to hook up and operate just as they do for Humming bird? Sure I do. The issue that I see (and have heard from people who switched) is that Motor Guide has a terrible hand control. What I mean is that they don't have a display on the control. There is zero way to tell if you are running the trolling motor at 3.5 capacity or 5.5 capacity (huge difference in battery life). Also, there isn't any indicators to tell you what mode you are in. You cannot look on the handheld and see that you are in GPS trolling mode, or Compass navigation. If you are in autopilot etc... In other words, it becomes a useless guessing game. The minn Kota remote gives you the clear ability to look on the screen and see speed, trolling mode indications, spot lock, auto pilot etc...
Many guys I know in the tournament industry that switched to Motorguide while using a Lowrance, used them for less than a year and quickly moved back to Minn Kota. They simply troll better!