If it is a Garmin unit only then 14 gauge wire to the battery will be fine. If it is a Garmin unit and a Livescope system then a 10 gauge wire will be required to the battery. You can connect the Livescope and display together on the same wire which will make your unit the switch for the Livescope module to turn it on and off. An in-line fuse is not required as Garmin's main power cable has the in-line fuse on it.
It is a garmin echomap 73sv. I was able to extend the wire with 18 gauge (per the manual) and connect it to the battery
I had to drill a hole through a tin like barrier between the battery dept and behind and under the drivers seat.
It is a 95 Bass Tracker 17 Pro.
I can't get the transducer cable ran because I can't figure out how to get the side panel off to run the cable behind it. I cant get to the rest of the screws because the drivers seat base is in the way.I took the screws out of the base and the base doesn't budge.I finally gave up and I am having someone put it in for me next weekend.
But I did discover the passenger seat come up and there were 2 very nice life vest's under it, a bobber and a cheaper life vest.