Boat wiring question

I bought a 3rd battery to run my electronics/lights/radio from rather than having them connected to my cranking battery. Why when I remove the +/- from the starting battery and put them on their own battery, do my volt/trim/fuel gauges not work? It seems like the +/- have to be in contact with the motor cables? My goal is to have a battery for main motor, and one for electronics but that isn’t possible if main motor has to be in contact with leads going to fuse panel?

The gauges themselves probably don’t ground but are connected to the ground wire that runs to the battery which in turn is touching the actual ground strap completing the circuit. Hope that makes sense. Run another ground strap off the 3rd battery to where the starting battery is grounded to the chassis(boat) and everything should work properly.

Ocean,

I don’t want to confuse this as Paul gave some very sound advice.

I have one question. Do you have the same number of + wires as – wires? What brand boat and motor?

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Do you have the same number of + wires as – wires?

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Good electrician advice there BK! LOL

I’ll expand for you Kev. I didn’t want to muddy up the thread if it didn’t pertain.

IF there were …

one red and one black motor wire
one red wire

Then we would know the ground is through the motor and hull.

There could also be a black wire going to the hull…which could easily be move to the new accessory battery.

I just installed a separate battery for my accessories last weekend and came across this very scenario.

There is always a madness to my method.

it should never ground through the hull……i have seen people try to put in aux lights and try it with no luck. i agree, double check for equal number of battery cables. depends on the boat but all the gauges and acc. should be wired to the “boats” battery supply. usually after a main breaker (usually 30-40 amp)

I would have been tempted to run a common ground.
Would there be any concerns with just jumping the two
battery negative terminals?
And then just let the positive connections determine which battery would service which components.

BK,
There is a +/- from the motor and then a + and 2 -‘s going from the battery up to the fuse panel I assume. I’m not sure where the 2nd neg battery cable is going? Would that possibly be grounded somewhere?
Motor is a 60 hp etec 2005
Boat is 1650 crestliner fish hawk 2005

My electrician skills don’t go much farther than touching a 9volt to your tongue to see if it’s still good

Assuming with boat, car or any wiring for that matter will at best lead you to a blown fuse. A fire at the worst.

Sounds like you don’t have an on board charger…correct?

You’ll need to trace those wires.

I do have an onboard charger but that is for the front trolling motor battery which is isolated from all this. I will trace the wires and see what it tells me.

To be continued….