Power Source
The good news is you have a problem that is constant, so trouble shooting will be easier. I was just looking over an M model, and the boat had two batterys, one for house and one for engine. Look at the cables running from the engine battery. They could have been removed (wisely) for the winter.Where are your controls? Is there a key switch? Near to that will be a fuse. Also, if wired correctly, the heavy cables to the engine will also have some kind of current limiter. There could also be some kind of connector with multiple pins that could have come apart just a little, but enough to cause a problem.All OK? Next you need to find the start relay on the engine. Hint: the red power cable from the battery goes to this spot. You will need a trouble shooting light or a voltmeter now. Is ther power at the red feed cable from the battery on the starter selenoid? If there is power there, I'd lean towards the key switch. If no power there, find out why by tracing back towards the battery. You can mechanically perform the job of the starter selenoid by using a single jumper cable to each of the large terminals on the starter selenoid, but I hesitate to recommend this procedure if you have no experience with heavy DC loads and the dangers and sparks and noise it can make. But by jumping over the selenoid, if no cranking happens, there is no power there (we already checked that), or your starter is inop. Let's say there is DC power on the feed side, and when you jump the terminals the starter cranks: then it is your switching that controls your selenoid, ie: the key switch.Good luck