Your post title says "installing", but the content talks about it already being installed? I'll respond, below, based on it already being installed because that's what it sounds like. In general, though, most things should not be installed direct to the battery. Only things like bilge pumps and ECM's, along with some stereos... but just the "station memory" feed.
A lot of this (well, ALL of this), depends on how everything is wired and whether or not anything has been altered over the years. Best way to check is to do it. Since it's your boat, what happens when you leave the key in the OFF position? Does your key turn one click CCW? Some key switches have an accessory position. At the very least, when you turn the key to ON, you are turning on more "things", such as gauges for example.
Often times, fuel pumps only run for a few seconds with the initial turn of the key, then they turn off and won't run again till the engine starts. I have no idea how it is on whatever engine you have. Like above, though, it's easy enough for you to check.