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.