Mercury outboard problem

Audrey II

Audrey II

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Aug 5, 2008
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I'm have friends with a 20 hp outboard on their dink we went for a ride two nights ago and in the morning the battery was dead and the motor was covered with corrosion. I figured it was a bad battery maybe a bad cell it wouldn't take a charge and it was 4 years old so it was time anyway. We replace the battery but it seems as though the motor is conducting stray voltage when the key is off. The motor runs fine but clearly there is an issue last night we disconnected the battery just to be safe but I'm heading over in a few with a volt meter to see if I can pin down the problem. I was hoping someone might has some advise as to what the cause might be.
 
Update I can measure both voltage and current from the negative terminal to the water around the boat another friend tried to clean some of the corrosion and said he felt a little bit of a shock while standing in the water and cleaning the motor.

I'm sure someone has seen this before please shed some light on this.

Thanks
 
sounds like stray current in the water from a shore connection. did they use an automotive battery charger??????
 
No it's coming from the dink! I think I may have traced it to the trim piston I did know what they where thinking designing an electrical pump that they feed the power from underwater it would seem it what only be a matter of time before this issue would occur. Being everything is running fine we will just lift the motor and disconnect the battery until I can get a closer look, I believe it is just a nicked wire on the power lead. The trim motor has content power even with the key out so this make perfect sense that it is the issue and it feels like the wire is chafed but until we pull it out it is hard to tell.
 
Well it's not the trim pump I disconnected both leads and it makes no difference. I did remove the ground going to the motor and this instantly removed the current draw. not sure what next.
 
quote:
Originally posted by Audrey II

Well it's not the trim pump I disconnected both leads and it makes no difference. I did remove the ground going to the motor and this instantly removed the current draw. not sure what next.

Click to expand...


I don't know if a DC clamping amp probe will show which gnd wire is flowing the current. I am not how low mine goes.
 
I tried to unplug every wire that could be unplugged and it continued to draw current the only way to stop the draw was to disconnect the ground wire on the motor which clearly is not a big help.
 
Does the positive lead from the battery go directly to the starter? Are there a couple of other wires attached to this positive lead at the starter? If so, I would disconnect all of them and test for current draw again. If you still have a current draw with only the starter connected then your problem is in the starter. If no current draw with ONLY the starter connected then it must be one of the other circuits causing the problem.

Mike
 
with the positive lead disconnected I dropped one lead of a multi meter in the water and touched the other to positive lead on the battery and I read 12volts when set for current I'm getting a measurable reading in milivolts but I shouldn't get anything. The new battery died within a couple of hours and the corrosion was crazy. I tried to unplug anything I could to try to isolate the problem but this only thing that completely kill the current was disconnecting the ground wire from the motor. This is very frustrating!
 
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