I have a 1969 crestliner Norseman. I believe it has a 120 4 stroke mercruiser. My battery has been constently draining so I narrowed it down to the main red power line that starts the boat. Even when I have the key off, when I touch the line to the battery it sparks. I dont think it is the key for when I turn the key on and push the START BUTTON it starts. to turn off, I turn the key to off and it shuts off. Why is it pulling? HELP PLEASE! Thanks!!!!

 

The heavy red starting cable should go from the battery to a stud on the starter motor solenoid. There it should be joined by a smaller 10 or 8 awg that powers all of the electrical devices on the boat. It may also be connected directly to the battery.

Pull that smaller wire off and see if the battery is still being pulled down. If it is, pull the fuses one at a time until you identify the culprit.

 

I wondered about a shorted diode in the alternator? Wouldn't that cause a similar issue?

 

It's not uncommon for the positive wire to spark when connecting to the battery. The electronics charge as soon as connected. Are you having a dead battery problem or is just the sparking your issue ?

Instead of connecting the red wire......connect a test light there, in series with it, instead. It should light up brightly when connected, dim and then go out.

 

Does the boat have any electronics, radio or fishfinder or even a gps of some sort. They all have the potential to draw down a battery if left for to long of a time. Quiescent draw is the expected draw in a later model car or boat that happens when keeping a memory circuit alive when the vehicle isn't running. As for a draw from an alternator sure it is a possibility but does that boat use an alternator of a stator as a part of the flywheel with a rectifier on the block. The test light test is a good one so long as you are looking for a larger draw, say one that kills the battery in a day or two, even a week but if it's a smaller draw the light won't see it. Just my 2 cents