Really weird electrical issue

[DanLieffring]

The past few years I've been having some strange electrical issues with my boat. First the voltage gauge went haywire and bottomed out. Then my engine alarm would randomly go off. Now the radio will power off and on. When I turn on the navigation lights, the gas gauge drops. I've changed batteries hoping that was the issue, but that changed nothing.
I finally got around to working on it all. So when my boat is on the trailer (not in the water) my electrical issues disappear and everything works as it should. The second the boat is floating, all the issues come back. Any idea what's going on? Why would the boat being in the water cause issues?
I'm going to try to put some 2x4's under the battery and see if having it further from the floor would help. Any other suggestions would be great!

 

[brodmann]

You've got a ground issue. I had a boat that would literally run in the yard, but not in the water. Had a 1976 55HP Evinrude on it. One day after struggling to crank it in the water at the boat ramp, I pulled it just out of the water, cranked it up and had my wife back me up into the water. Once the boat was halfway in the water, the motor shut off and wouldn't crank! I called my boat mechanic at home on that Saturday afternoon and explained it to him. He told me exactly what wire to disconnect and told me the motor would run all day, but I'd have to re connect that wire to shut the motor off. I took the boat to him a few days later and he replaced the wire. The insulation was worn through on one section of the wire. I'd check all wires on the motor to make sure everything is tight. If all of your accessories are "key on" wired, I'd rewire or replace the key switch. I'd also check the connection of the negative wire from the battery to everywhere it goes and everything that is connected to it or branches off from it.

 

[Chris1956]

Not sure about the precision of post #2. He is talking about a short from the ign killer wire to ground. Not sure that is your issue.

I do think it is a bad ground wire. It would be best to clean and inspect all ground wires. It appears that both power to the engine is affected, as well as power to the gauges and lights.

Also, look for wires laying in the bilge, as they can get wet, and if the insulation is nicked, that can short thru the water to ground. I don't think that is your issue, but while you are inspecting the ground wires, check for any power wires in the bilge water.