Installing NMEA

I ordered all the parts to install the NMEA 2000 from my Garmin 93V to the Honda 115 yesterday. I was thinking of using the power from the gas gauge that is switched on from the 115. On my old boat I had a Lund 1775 there was a master power switch on the dash . This Pro-V, Hewescraft doesn't have a master. On the Lund I had Hondas 90 & 8 the gas gauge was power by the 90Hp. So when using the 8 Hp the gas gauge was not powered up. I rewired it so that whenever the master was on the gas gauge worked. Using the same thought the NMEA powered from the hot side of the gas gauge would only be on when the 115 is running. So whenever the 115 is not running the NMEA is not powered on. If I am trolling with the 8HP I could just turn on the power to the 115 to get a read on the gas level. Or rewire a master switch like I had on the Lund and power down the NMEA , and rewired Gas gauge powered from the master. Lot more work would it be worth it ????