Trying to start my 260-M the starter...

[GooseTx]

Trying to start my 260-M the starter wasn't turning over the engine then I noticed smoke coming off my negative battery post?  I took the starter to a auto parts store and it tested Ok.  What else would cause this problem?  The boat flooded in my driveway when we got 5 inches of rain one night and I didn't realize that the plug was in so the starter was under water for about 8 hours before I noticed. 

[wingless]

The easy solution is to launch the boat w/o first installing the garboard drain plug, then go park the truck and trailer.

Otherwise, the problem is easy to fix. The engine starter is almost always the greatest current load on the boat. Every single connection in that high current path must have clean and tight connections.

The no start smoke was caused by a dirty, or loose, or both connection.

The best option is to first remove all battery negative terminals. Then sequentially disassemble, inspect, clean, reassemble and properly tighten each connection in the entire loop from battery positive to battery negative.

The factory service manual for my Mercruiser specifies liquid insulation on the connections, so I seal them w/ liquid rubber.

[GooseTx]

Thanks wingless!! I like that Liquid insulation? Guess that's not the best way to maintain an electrical system. I'll look into the liquid rubber.

[wingless]

YW

Here is the product I use to comply w/ the Mercruiser FSM after everything is clean and properly tightened.

http://www.starbrite.com/item/liquid-electrical-tape?category_id=568

My boat was manufactured w/ some spray on amber colored insulation over all the exposed electrical connections. My guess it the factory used Cosmoline or an equivalent.

https://en.wikipedia.org/wiki/Cosmoline#:~:text=Cosmoline%20is%20the%20genericized%20trademark,time%20with%20exposure%20to%20air.

[quack]

Read wingless suggestions, all good advise. But read your problem and you said the eng. won't turn over. Is it possible water got into eng, have you tried to turn it over by hand?

[High_priority]

Pull the spark plugs and turn the motor over. If water gets in the cylinder it will not turn.