My outboard when warm will sometimes act like the battery is almost dead. Starter will engage but cannot turn over engine. When it works correctly I can read over 10 volts at the starter. When it doesn't I only read about 5 volts. All connections seem to be ok and I have two new batteries. When it does this, I can hit the key again and within about 2 tries it works ok. Does this sound like a bad starter or could it be the magnet switch?
Have you tried direct from battery to starter terminal(s) using a set of
jumper cables? It is either the starter of something else...if starter problem
persists it is likely the starter...if the problem goes away it is likely
something else. If a problem is one that comes and goes it gets a little
more involved, but, this is where I would start.
Bear in mind that metal conducts and metal oxides insulate...years ago a friend
drove his car to school. A few hours later it would not even attempt to
turn over although headlights worked. I suggested the battery posts
although they did not look bad were the problem. The road service mechanic
cleaned clamps and posts and car started right up...lessons in
that for which I did not have to pay...Preventative Maintenance, have
some basic tools in car for emergencies...and keep extra money in back
of wallet as you never can tell when you will need cash.