Bizarre electrical problem on a Mastercraft

[Ron V]

Hey guys, a little off topic but thought that with all of the great minds here, someone might have a thought that would shed some light on this. Here are the facts and sequence of events.

Boat is a 2000 Mastercraft ProStar 195. It's a 5.7 Chevy, throttle body injected (I think it's a PCM engine).

Was supposed to go skiing with a friend, and she called me from the marina to say that everything was completely dead, even though she was quite certain that every switch had been turned off when she left the boat. Auto bilge pump was off. Battery apparently completely dead. So I said I'll bring a fresh battery and we'll jump it.

Tried jumping it, would barely turn over. Apparently too much current loss through the cables. Plus it calls for an 800 CCA battery and my spare was 560. Our third skier tried jumping it directly to the starter and a ground on the engine with the ignition turned on. Didn't work; gave up after about 2 seconds.

So we pulled the dead battery completely out and put the new battery in. He noticed a spark when connecting the negative cable. Not a mild static discharge, but a notable spark. That's not right. Engine turned over slow but started after a couple seconds. Within 5-10 seconds, smoke was coming from under the dash so we shut it down and quick disconnected the battery. Battery went from green to black just from the couple of attempts.

The ground wires on the main electrical harness under the dash are cooked, along with several other ground wires in the boat.

The guy who winterizes it for her checked continuity in the ground from the engine to dash and didn't find any problem there, but then again you really can't wiggle the harness under the floor to check for breaks. His best guess was that a loose ground on the battery led to all of this. He also said he's seen this kind of stuff because of jump starting in the past, but was a little perplexed that the smoke didn't start until after we had completely swapped the battery out and started it.

I say jumping it is like running two batteries in parallel, and not even, since one battery was totally gone, so how is that going to damage anything. Also, SOMETHING caused the battery to drain, SOMETHING caused that spark when the ground cable was connected, and I also doubt we ran it long enough to cook all of those ground wires that bad from that alone. My suspicion is a dead short somewhere in the boat, but why didn't everything burn up and torch the boat while it was sitting at the pier?

Original battery was checked. There are no dead cells, but it was only about 2/3 charged after two days on a 1.25 amp trickle charger.

OK guys, have at it. We're stumped on where to look or what happened. Thanks.

[H2OPERF]

You may have an issue with the main battery cable ground and it was trying to ground thru the smaller accessory ground wires from the battery to the panel..

[JR IN JAX]

Did someone reverse charge the battery?

[Ron V]

Did someone reverse charge the battery?

No, the fresh battery had been on my maintainer on a timer so that it would come on once a day for an hour or so. Battery was totally green and I never got an error light on the maintainer, which would alert me if I hooked it up backward. The battery that went dead in the boat had been in there and running all season.

[Michael J Giesler]

Hi Ron when I worked for lakeshore marine we had a Mastercraft 190 with the corvette Lt1 had a similar problem ended up being bad cables green on the inside cheap fix but took half the summer to figure it out the ends looked perfect but junk inside