Squirrelly Electrical

[Shannonsj]

So I’m cruising along happy as a lark in the SS Minnow (name changed to protect the innocent) when the entire DC system went dark. Engine kept running just fine...and alternator seems to charge, but nothing DC works. All the gauge needles move and jiggle happily, but all are reading wrong. Engine even starts easily. The “Minnow“ is a ‘76 F26, but it was repowered with a 310hp PMC 350. I think new gauges came with that engine.

Where do I start the major surgery?

[The Dog House]

Since everything went dark at the same time I would guess you have a bad ground connection somewhere. I would start at the fuse panel, but if you want to be methodical you can start at the battery and work your way forward. When I bought my boat the fuse panel had a lot of loose connections. The PO had used a house wire nut to tie together several ground wires. Needless to say the components attached to those ground wires only worked intermittently until I solidly connected those to the fuse panel.

[Shannonsj]

I was so afraid someone was going to say “ground problems”

You should see how ugly that ground block looks

Thanks brother!

[prowlersfish]

X2 on the grounds and check any breakers you may have .

[WayWeGo]

I came across a nice tool for working on electrical systems, the Power Probe 3. You hook it to the battery with clips and it has a probe tip that can be used to measure voltage, or also to provide ground or 12V to a circuit. Its kind of like a test light on steroids. While it is not cheap, it is well made and makes troubleshooting power and ground problems a bit easier. It has a 20' lead and the version I got comes with an additional 20' extension which makes it nice for working on boats and trailers.

A professional mechanic friend told me about it and I couldn't resist.

[Shannonsj]

Stop it

Now I think I have more money in my magic tool box than I have in the boat.

Just kidding. I had to have one. So I do now. As soon as that Amazon chick delivers it. I hope she’s cute.

Someone’s gonna hafta buy this boat tho so I can pay for all the sweet tools I’m buying to get it ready to use

[10meterman]

You will use the Power Probe a lot ,,,worth the money ,,, first thing I grab when I'm having DC power issues
Boats , lawn tractor , motorcycle ,, 40years of freaking cars

[Shannonsj]

$70-ish on Amazon. Apparently there’s a couple of newer models, so I lucked out finding this one cheaper.

I can’t wait to play with it now.

[Shannonsj]

New symptoms...

With the key off, the 12VDC bus reads 13VDC.
When I turn the key on...it drops to 8 VDC. Engine isn’t running...just the key on.
Why would that happen? I’m convinced there’s definitely a ground issue or the lights and everything would work fine...but this is a new one.

[prowlersfish]

It is dropping because of the increased load of tuning on the key . What is it voltage of the battery with the key on ? If its ok then check voltage fro battery ground to the 12 volt source that is dropping voltage . Do this with the load on .

[Shannonsj]

Battery voltage (at the battery) is normal with key on or off. Turn key to “run” and the 12v bus/fuse panel.... where all the electronics (and bilge pumps ) are connected...drops to 7-8 V.

Literally every single dc electric device is affected. Nav lights, gps, bilge pumps, and on. But the engine starts perfectly every time. Weird.

Sunday I’m going to replace every crimp connector on the ground bus. They are all skeeery looking.

There’s another terminal block beside the ground bus that looks even worse...so I’m going to replace those too. That one is a mix of ground and 12v connections.

[prowlersfish]

That's why I said to check voltage from the battery ground terminal to where you have low voltage . If it reads low then you have a issue on the power side , If it reads normal then its a ground side issue . Again do with a load on .

[Shannonsj]

I traced the primary ground wire back from the ground bus to a large plug behind the engine block. All of the connections were really oxidized and kind of furry looking.

I used my dremel and a soft wire wheel to polish all the posts and then a small round file to clean out all the sockets. Worked perfectly. Now I have a boat again .

I’m still going to clean up all the terminals on both busses though.

Thanks for the help everyone

[The Dog House]

Glad you found the problem and were able to fix it. Thanks for posting the resolution. That knowledge sharing is what makes this forum so valuable.