I have an 03 326. Currently instruments are ST40 (depth & speed and an ST60 wind meter). Power goes to wind meter and seatalk plugs provide power to other two instruments. Can I splice into power line running to instruments to install a Garmin GPS. I do not want to run a line through boat to fuse panel. Their is three large gauge wires in pedestal that do not have power (maybe for windlass or autopilot which I do not have). Any suggestions.