Mariner/Tohatsu electrical problem.

[Jarrah Jack]

I've got a 2001 40hp Mariner and I've just discovered that the neg to the motor is'nt isolated. I'm getting a stray neg currant throughout the tinnie which isn't a good thing I've read on here.

I've tracked the problem to the main neg lead that is connected to the starting motor. When I disconnect it the current goes. Should the starting motor be isolated or is the cause something else concerning the control unit. I would've thought that with the key in the off position there should be no pos or neg current going to the motor.

[Spaniard_King]

Jack,

best scenario is to isolate both positive and negative, but this should not be necessary. you obviously have something drawing power through the battery system somewhere, it may not be associated with the engine but it maybe using the engines earth as part of its circuit

[Jarrah Jack]

Thanks Garry I was hoping you would respond. I was thinking of isolating the neg with a simple battery switch. The pos already has its own. It must be something to do with the motor though as I can disconnect everything else and still get the stray current? Cheers Terry

[Fed]

I'm getting a stray neg currant throughout the tinnie
How do you know this?

[Jarrah Jack]

How do you know this?

I tested with the multimeter after I got a short doing some wireing by letting a pos touch the dash. Fixed a pos wire from the battery to the meter then hit the boat with the neg.

[Fed]

Well the negative is always connected to the motor and the motor is always connected to the hull so you'd expect that result.
In fact that also allows your outboard anodes to offer some protection to your hull too and it is impossible to bolt a motor on without it being electrically connected to the hull.
The problem comes when you have more than one negative connection.