Not sure how the 360 is set up, but if it is similar to the 330, (and a previous owner has not muddled with things) the stereo power comes from the main AC/DC panel in cabin. Remove this and validate that the switch is good. If switch is good, and it is wired as mine is, the problem is between the switch and the radio.
Has work been done on the boat recently? Did the radio work previously? More background will help us provide advice.