Battery switch troubleshooting

[Thekaj]

Last summer we managed to blow an engine on our 1995 325 Aft Cabin. One of the things the mechanic noted when he was done was that he had switched the battery switch to off and still got shocked. With electrical not being my forte, I called in another mechanic a couple weeks ago, who decided that the (two battery) switch had just worn out, and stuck on. He walked me through how to replace it, and I decided it was simple enough. Got the new one, transferred the wiring one at a time, making sure the all went on the same poles. Switched it to off, and all the DC stuff still stayed on, including being able to crank the engines.

I plan on going back down with a multimeter to do a bit more scientific testing, but any thoughts on what the issue might be? It’s not exactly a complicated system. Besides the battery cables themselves, each battery pole has a voltmeter wire attached, and that’s it (bilge pumps attach at the batteries). Neither the mechanic nor I can see any odd bypassing going on. My only thought is that maybe someone mixed up the cables at some point and swapped one of the battery cables with the output. I just don’t know how that would still make “off” not work.

[Phrancus]

Hard to say without details and lots of possibilities and impossibilities that readers can throw your way.

My approach would be to disconnect as much as you can and the build it up while double checking everything. I do that with a long wire into the engine room and check wire per wire for trouble. So first check if every cable is still a single connection (if there's a problem along the way from engine room to switch you want to know that early).
Then check the connections, you may have a 'bridge', an unwanted connection because of damage or a faulty device like an altnerator that shorts but in such a way that it still works.

Then start connecting batteries to engines to make them work, then you include the switch in the set up.

Note: do not disconnect batteries from the engine while running, this damages the alternator.

Tip: you might want to use a smaller, separate simple battery for testing and include a small fuse in the testing wire. So you don't work with the big amperages when testing and not damage anything when you short the cables by accident (get more fuses)

Tip: you might consider a small lamp (12v led or something) to use for testing. You can see it connect or not from a distance. Handy when you're in the engine room probing away and these modern meters often turn themselves off, or beep at strange moments and have displays that you can't read from where you are.

Last tip: make a drawing, a scheme so you know what you tested and also for future reference. Mark the cables at both ends and document it. Easier to ponder over while at a table and a coffee rather than having to remember it all while getting stressed out because the meter quit, the cables are too short, a connector you just tested turns out not to have connected after all and so on.

enjoy the search

[Viper]

Almost sounds like the switch has been intentionally or unintentionally by-passed. This is easy to do by hooking up the load wire from the panel directly to a source terminal on the switch where a battery is hooked up to. If one or more source cables from the batteries are connected to the load side of the switch along with your load wire to the panel, the result is the same and shutting the switch off won't do anything. There'll still be a direct connection to power as this by-passes the switch.

You need to confirm that your battery/source wires are hooked up to the source terminals on the switch and your load wire going to the breaker panel is hooked up to the load side of the switch. No wiring should be bridging the source and load terminals.

[Phrancus]

Agree with Viper: In the end it will turn out to be a simple mistake, it needs only one wrong connection to bypass safety measure.

You may very well have taken the effort of switching off and on dilligently when leaving and entering the boat while in the meantime there was a permanent connection....