Really need more information, such as boat mfg, motor mfg, year of boat and motor. Can't help you with the information you provided and may not be able to help even if you do provide the information.
If you have no idea what it is, where would you plug it in? The question for you is "what doesn't work"? If everything is working, it is obviously not needed and very likely is for an accessory your boat doesn't have. If you look closer you will probably find more unused connectors or wires. Follow the wire from its end to wherever it goes. That would help to determine what it's for.
Does the alarm stop after a couple seconds? If so, it is your smartcraft alarm system and you should leave it plugged in. It'll go off when there is an issue with the boat.