boat ground?

[ib_jigged]

I have a question regarding ground on a boat. I have a 2010 Lund Rebel 1725 XL Sport with a 90 hp 4 stroke merc and am trying to hook up a trim gauge. I figured out that my starting battery (which also has all my electronics connected to it) is isolated from my motor, which is grounded to the hull.

Should my starting battery also be grounded to the motor and hull? Would my starter not want to find the path of least resistance to try and ground to the battery when starting?

If not, I will have to run the ground of the trim gauge all the way back to inside the engine compartment.

When I spoke to my Lund dealer yesterday about connecting a trim gauge, they said it was simple just connect power and ground to 12V source behind the dash and connect the trim indicator wire to the gauge and I would be good to go. That leads me to believe that the battery should be grounded to the motor and hull.

Anyone have any experience with this?

Thanks,

Del

[fishingstar]

I have a ground strap running from my battery to the ground strip on the hull of the boat. I had a lot of electrical problems before I did this.

Dan

[Esox_Magnum]

Ground post on the battery is your ground. Your outboard ground is tied to the battery.

[delcecchi]

The whole electrical system "ground" (not counting trolling motor) is the black wire that goes back to the battery. As I understand it, using the hull as a ground can cause corrosion problems, especially when charging the battery, or any time there is stray voltage around while the boat is in the water.

If a connection from the battery to the hull was a good idea, I think Lund would have put one in.

[CAMAN]

Yup never ground the hull. Always run a separate ground wire to each component. Electrolysis can be a very bad thing on an aluminum hull.

[LMITOUT]

Ground post on the battery is your ground. Your outboard ground is tied to the battery.

What he said.

You should not have any electrical "grounds" connected to the hull of your boat. All ground wires should be connected to the negative terminal of the battery, either directly or to a bus mounted remotely so that you don't have to run every wire back to the battery.

If you look under the dash you will probably find a ground bar or connection point where all the electronics have their negative terminal connected. From this ground bus there will then be a wire running to the negative terminal of the battery.

Yes, the engine is physically connected to the hull of the boat but it is not a ground. The starter has a +12V and -12V connection and those wires go to the battery. If you look at the bottom of the lower unit you will find a sacrificial anode which is where any voltage that builds up on your boat is bled off, sort of speak. This prevents the metal of the boat from corroding just from the natural charge that a boat acquires moving through the water. By connecting your electrical system to the boat you're just adding to the problem.

[ib_jigged]

OK, I understand this, but my trim sending unit is grounded to the motor, and the motor is isolated from the battery. Therefore, I do not get a signal to my trim gauge by grounding to the battery. The negative terminal on the battery has no continuity to any bolt or the trim sending unit ground wire on the motor.

[boatfixer]

Your motor is not isolated from the battery. There are 2 large cables that are attached to the battery. The positive is connected to one side of the solenoid, the other is the ground which connects to the block of the engine.

[Surface Tension]

I'm not following you but here.

There is a pair of - negative and + positive cables that runs from the battery to the outboard.

The + cable will go to the starter solenoid and the - to either the starter or block of the outboard. Note that there is - to the block of the outboard and the outboard is bolted to the hull so yes the hull is - there BUT you wouldn't use the hull for a - connection to any accessory, instead you'd run a - wire to each of them.

You should also have a pair of wires - and + that run from the battery to the counsel. The + will go to a fuse block or breaker panel for lights, live well, bilge, accessories and so on. Somewhere near by will be a post for the - that is isolated from the hull.

Connect the - to that post and the + to an open spot on the fuse block. If there isn't an open spot on the block then add it to the point when the + cable connects and add an inline fuse close to that connection to protect the wire.

[ib_jigged]

OK,

A little more digging. The trim sender is grounded to the lower unit/cowling, which is NOT grounded to the power head, which is grounded to the battery.

The lower unit/cowling is grounded to the hull, the power head is not.

Does any of this make sense? It really is starting to make me wonder why connecting a trim gauge is so hard.

If I move the ground of the trim sender to the powerhead, everything is OK. I just need to solder a longer wire to the ground lead of the sender and run it with the BRN/WHT wire into the cowling and pick a location on the powerhead to ground too.

It would have been much easier had Mercury just ran both of the wires of the sender into the cowling and connected the BLK wire to a ground in the harness.

[delcecchi]

OK,

A little more digging. The trim sender is grounded to the lower unit/cowling, which is NOT grounded to the power head, which is grounded to the battery.

The lower unit/cowling is grounded to the hull, the power head is not.

Does any of this make sense? It really is starting to make me wonder why connecting a trim gauge is so hard.

If I move the ground of the trim sender to the powerhead, everything is OK. I just need to solder a longer wire to the ground lead of the sender and run it with the BRN/WHT wire into the cowling and pick a location on the powerhead to ground too.

It would have been much easier had Mercury just ran both of the wires of the sender into the cowling and connected the BLK wire to a ground in the harness.

Now that is strange. How could the power head be isolated electrically from the lower unit and cowl? Is some stuff plastic? Is there a missing connection from powerhead to something, sort of like the ground strap to frame on a car?

[boatfixer]

It's grounded

[delcecchi]

The guy with the problem said it isn't grounded, and that is why the trim sender doesn't work. What is the matter with this picture? I guess I don't know from what has been described. My merc trim sender worked fine.

[ib_jigged]

Just checked again last night. My motor mount area where the trim and tilt unit and the trim sending unit is mounted is not electrically grounded to the engine block. Neither are the motor mount bolts. The trim sending unit is grounded to the motor mount, bolts and hull, but not the engine block itself where the battery is grounded.

I am going to remove the ground wire for the trim sending unit and solder an extension on to that and route it into the engine compartment and ground it to the block and everything will be fine.

If it were grounded together, the battery negative post would then be grounded to the hull.

Del

[Ice Wolf]

On a tin boat should you not bond the (-) to the block of the engine or to the hull of the boat to prevent stray voltages ? What if a (+) wire got pinched to the hull. You would not blow a fuse. I am not saying to use the metal hull of the boat as a path for currant to your equipment but to bond the (-) to the metal of the boat so you have a path for fault current to take?

[FM_Mike]

When I spoke to my Lund dealer yesterday about connecting a trim gauge, they said it was simple just connect power and ground to 12V source behind the dash and connect the trim indicator wire to the gauge and I would be good to go. That leads me to believe that the battery should be grounded to the motor and hull.

Anyone have any experience with this?

Thanks,

Del

I know this probably doesn't help, but if it's as simple as the dealer says it is, why not take it to the dealer and have them set it up for you?

If it is as simple as connecting the wires, I'm sure that the cost of having them do it should be minimal. Also, if there's an issue, the dealer could most likely diagnose the issue quickly and you would not have to take a chance of improperly wiring.

Sounds like, based on what your finding, and what the dealer has told you about the simplicity of this, you may have a wiring issue that may need to be addressed.

Mike

[ib_jigged]

The dealer I bought the boat from is 4 hours away and when I call the next closest Lund dealers to me, which all three are equally about an hour away, they ask if I bought the boat from them and then when I say no, they say the will call me back and then I never hear a word from them.

I guess that is what you get when you live in the only county in the Land of 10,000 lakes, that does not have a lake!

[delcecchi]

My mercury service manual only goes up to 2002 but I am starting to wonder if the remote wiring harness is hooked up correctly, inside the motor. The diagram I have shows a brown and white wire that goes from the harness connector to the trim sender. There is also a tan wire that is on the "starboard side" of engine" that gets plugged into the harness, in addition to the wires in the connector. The brown and white wire on the other end of the harness goes to the gauge, along with black and purple.

I think the tan wire is a temperature sender.