It's very simple to add. Just order it. You attach it to your TM or transom, whichever you choose, then run the lead back to the unit and there is another terminal bay to plug it into. That's it. When you turn the unit on again, it auto runs a diagnostic and adds the temp sensor. It will beign working. Good luck. I bought a $15 MARINE temp sensor at Wal-Mart and glued the sensor to the bottom of my TM, then ran the wire, mounted the LCD next to my graph on the bow, (all took about an hour) and when it got WET from the rain, it died. A MARINE TEMP GAUGE for cryin out loud. Anyway, have fun.