Entire electrical system dies when under way

[peters715]

When the engine is running, any RPM, and I turn on the exhaust fan, bilge pump or trim, the engine dies and all electrical power shuts off.

I turn the battery switch to off position then back to battery 1 or all battery and then I have power again and usually able to start the motor again. Sometimes the starter cranks for a quick second and power goes dead again.

This just started happening and got it off the water immediately.

Battery is only a few months old and is on a charger 24/7. Cables are good.

Stumped to say the least.

 

[Chris1956]

Well, your electrical cables are likely not good, somewhere. Look for corrosion under the insulation. Check the battery switch for corrosion. Remember it does not take too much resistance to cause voltage drop on a 12V system.

 

[jlh3rd]

+1 on corrosion somewhere. I had a similar issue a year or so ago. It turned out to be a corrosion issue in the battery feed (wasn't the connections) to the ignition switch. Drove me nuts as it was intermittent and never totally shut off my motor but it would stumble.
I discovered it when moving the wire feeds around at idle, removed the wire wrap, began tracing the ignition red feed wire and found the partial break/corrosion under the wire's insulation.

 

[peters715]

Thank you all! The battery to switch cable had a lot of corrosion at the switch. The switch connection was melting too.
So I replaced both cables. Both were 4 gauge and the battery to switch was pretty bad. Upgraded both to 2 gauge. And put marine grade heat shrink over the seam where the cable crimps into the connector.

Probably would have been ok with 4 gauge but err on the side of caution.

 

[peters715]

Also I replaced the switch. All new gear from battery to starter.

 

[redneck joe]

so was that the fix or you have done that and still happening

 

[Scott Danforth]

I would start at the battery and check every connection (both power and ground) all the way to the helm and every thing that receives electrons.

a melted switch means that there was a really really really bad connection and the arcing of the connection caused enough heat to actually cause a fire.

 

[peters715]

Replacing the cables and the switch solved the problem. The starter is more vigorous and the system does not die when I turn on an accessory.

The alternator output drops and engine rpms drop (probably less than 50 RPM) when I turn on the bilge pump, system doesn't die, but it's noticeable.