Where is the Ground?

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garyvoss

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Grady White Marlin 2006. I have disconnected all the ground wires (but not the engine earth) from the battery, but my bilge pump still operates in automatic mode. This suggests that the bilge pump is grounded to the motor somehow? Can anyone shed light on this interesting quirk?
 
Download the GW Owners Manual from GW site. Look at the wiring diagram. Will show how bilge pumps are wired and fused.
 
Hi Hookup1. I have done this. My drawings show only the positive sides - not the ground. The ground is just shown as a ground symbol - where the wires actually run or connect is anyones guess!
 
On my boat they are direct to the battery. Positive sides are fused. Get back there and follow the wires. Take the miscellaneous black wires off one at a time. On my boat they connect to an automotive style battery terminal. I installed them to keep the connections together when battery is disconnected for replacement. The positive wires go to the hot side on the back of the DC switches. In-line fuse is near the aft pump underneath a shelf above the pump (terrible location). Not sure where the fuse is for the forward bilge pump (may be next to the aft one).

Screenshot 2025-07-20 at 7.48.48 AM.png
 
garyvoss said:
Grady White Marlin 2006. I have disconnected all the ground wires (but not the engine earth) from the battery, but my bilge pump still operates in automatic mode. This suggests that the bilge pump is grounded to the motor somehow? Can anyone shed light on this interesting quirk?
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How many batteries and did you disconnect them all?
There should have be a blach smaller guaage cable connected to one of the battery negative terminals in addition to the fatter black cable. The smaller size wire is the main ground for accessories.
 
My Canyon has a automatic Bilge Pump fuse with the +12V cable on the battery switch panel, but not sure where the -12V is connected.
You may check somewhere there where the battery switches on your Marlin are, there may be another -12V bus bar.
Chris
 
Are you saying that the bilge pump is running constantly?

Or, it actually sounds like you want to disable the auto function? If that's the case, why?

But... just remove the fuse (or flip the breaker) for the auto side of the pump.

If you remove the ground... won't you also be eliminating the manual control of the pump? In "most" cases, there is a single ground with two hot leads.

Oh... you said you disconnected the grounds from the "battery"... don't you have more than one battery?

Does one of the battery's have a ground that goes to a bus bar? I can't say what is going on with your boat, but best practice is that accessories are NOT all grounded via a battery terminal... instead through a common bus bar. Look for that.
 
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Thanks for all your responses - I have read and digested them. I have since done some more checking. ALL my house systems work even if I disconnect the "house" negative from the battery. The negatives are finding their way back to the engine cabling since that is the only cabling still attached to the battery. I really need to understand where the earths are all connected as I fear I may have some sort of dodgy connection somewhere that may cause nasty electrolysis etc! There is no way of tracing the wires - they are all in conduits inside cable ducts and only God (and Grady White) know where they are all terminated on the negative side.
 
Your going to have to live with the mystery...get over it.

If it bother you that much re-run the wires - mystery solved.
 
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Hookup1 said:
Your going to have to live with the mystery...get over it.

If it bother you that much re-run the wires - mystery solved.
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I am trying to install a Victon battery monitor. It has to be installed on the negative return to the battery but it seems that power is sneaking back from all my devices through the engine cables rather than the main negative. Hence my eviction does not work. Tough to live with. Just need a diagram of the earths I suppose.
 
garyvoss said:
I really need to understand where the earths are all connected as I fear I may have some sort of dodgy connection somewhere that may cause nasty electrolysis etc!
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Be very careful with that!
Back in Costa Rica my captain connected the -12V battery cables wrongly to a unused cable of a old shunt and engine was discharging in water thru outboard leading to electrolysis. You should check that asap to avoid major problems!

I would first look elsewhere than the cables in the conduit as it's least likely that the problem is there, more likely that a -12V is connected wrong or not connected.
Take your time, make a diagram and check negative cables on battery posts, in cabin -12V bus bar and transom area if there is another -12V bus bar (i had one made by a bolt screwed in a wooden bulkhead)

A useful tool is a long cable with a ring terminal and/or clamp on one end and a multitester to check continuity between cables and bus bars
Check if electronics are working if engine battery cables are completetly disconnected, including engine harness power cables (if any).
If Electronics or some of them don't work anymore then common ground is your outboard/s and thats bad.
Check also if ex owner installed a under water anode where grounds are connected.
If you have limited experience with electricity and/or using a multimeter for continuity and maybe ohm meter then i suggest you to call a boat electrician.

Chris
 
As Chris stated there is a good chance something is miswired. On my 1997 Islander all wiring was original, unhacked. What I hated most was all the miscellaneous ring-terminal wires that connected to the battery terminal. Some are not color coded (like green wires for the original Yamaha fuel management gauge and fuel flow sensors. When changing batteries over the years it was too easy to forget one or mix them up. I would tie wrap together thru the rings. To clean this up I installed automotive style battery terminals. Now the only individual connections are the engine, A/B switch, charger and ground jumpers.

The engines should be the easiest to isolate - the two heave gauge cables. But my boat the fuel flow management gauge and fuel flow sensors are connected to the engine and to the battery + and - with bundles of green wires. This creates a ground return thru the gauge wiring. My point is ground returns like this are not going to be documented.

In the case of you bilge pumps there has to be one or more cables suppling ground to the bilge pumps. Take every ring terminal connect off/apart and test them one-by-one.
 
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garyvoss said:
Thanks for all your responses - I have read and digested them. I have since done some more checking. ALL my house systems work even if I disconnect the "house" negative from the battery. The negatives are finding their way back to the engine cabling since that is the only cabling still attached to the battery. I really need to understand where the earths are all connected as I fear I may have some sort of dodgy connection somewhere that may cause nasty electrolysis etc! There is no way of tracing the wires - they are all in conduits inside cable ducts and only God (and Grady White) know where they are all terminated on the negative side.
Click to expand...
You should isolate what is the ground source. Try the following.
Place all battery switches in the OFF position. If anything other than auto bilge and possible stereo memory feed works, you sill have accessory power connected. That could be a bad switch or perhaps a ground accessory wire that is connected to ground somewhere. Common sources of phantom grounds could be the ground buss at the helm fuse block or a ground bus bar at the helm That can happen when a motor harness ground wire from the engine is mistakenly connected to the accessory bus bar at the helm. Typically that is caused when the motors were rigged and the installer mistakenly connected a motor ground to the accessory ground.

There may be a load that is always powered when it shouldn't be. If that is a heavy load, its low resistance can act as a secondary ground. In theory any such device would be fused somewhere. This is more likely if the batteries are running down more quickly that one would expect when the boat is not being used.

Unfortunately, you may need to totally disconnect all batteries and then reconnect one at a time to see if when the problem with the phantom ground shows up. Label everything and take pictures if you can.

Finally, if you boat using bonding on things like sea cocks and external zincs, you may have a a situation where the bonding is wired incorrectly. This is a bad situation that can result in significant electrolysis damage.
If you have and use shore power, disconnect that at the boat and shut off all AC breakers before the battery testing.
Do you have an onboard battery charger/maintainer. If so disconnect charger grounds and verify wiring/charger operation.
 
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