1997 Lund Pro-V 1800 Fuel Tank Ground?

[bladpart]

We have a Lund Pro-V 1800 from 1997 that's had some electrolytic corrosion issues we've been sorting out. Details below, but the simple concern here is that we've noticed that the fuel inlet (where you fill the gas tank) has a green ground wire connected to the fuel tank's sender. This is creating a ground to the boat's hull. Additionally, there's a black wire (part of the pink/black combo meant for the fuel sender->gauge connection) that's connected to the fuel sender that connects to the negative post of the battery. It's spliced to the same ring terminal as the green wire. This ring terminal with the black and green wires is screwed into the fuel sender.

Now...that seems counter-intuitive to me. I assume the green wire is necessary to alleviate sparks causing a fire when filling the tank, but I guess we're surprised it's connected like this. To my knowledge it came that way from the factory. Maybe someone can help me understand what's going on there? With the fuel sender return wire coupled to the green wire and then to the hull, isn't that going to cause electrolytic corrosion? The black wire connects to the negative battery post, so now aren't we creating a direct path to the hull for all the accessories connected to the negative post of the battery instead of through the motor? I any grounds to hull needed to go through the motor.

Some back story. Last season when my folks pulled the boat out of the water (they keep it in the lake at the dock for a couple of months), they noticed pin holes in the transom. Long story short on this, after mostly ruling out a known issue with the copper imbued wood of the transom (galvanic corrosion), it seemed like the problem was electrolytic corrosion. One of the accessory wires running to the battery terminal was shorted to hull, and we figured that this was the cause of the developing pinholes.

Now, the way Lund ran this return wire wasn't great, it was spliced in a couple of accessible areas with the negatives of several accessories instead of having separate negative wires connected to a terminal block or directly to the battery. We tried to isolate which accessory was causing the short and ended up just cleaning up the wiring. Added a terminal block near the battery in the back of the boat, and ran 12AWG marine wire for everything that needed it. Everything checks out as open-circuit or a high enough resistance...all except that black wire for the fuel sender which of course is grounded to the hull directly via that green wire I described above.

[Ltrain]

Definitely a no no using the hull as the return path . You are correct to assume that this would be causing your corrosion issues. I would eliminate that green wire.

[Hot Runr Guy]

the need for the bonding wire between the fuel fill and the tank depends on whether you have a metallic fuel fill (bonding required) or a completely plastic one (bonding not required).

I'll bet you a case of beer that even if you delete the bonding wire, you will still see continuity between your tank and the hull, due to the mounting bolts of the outboard. It is next to impossible to isolate the outboard negative side from an aluminum hull, so unless you're willing to remove your outboard, you can expect to see a ground path.

HRG

[Ltrain]

Originally Posted by Hot Runr Guy

the need for the bonding wire between the fuel fill and the tank depends on whether you have a metallic fuel fill (bonding required) or a completely plastic one (bonding not required).

I'll bet you a case of beer that even if you delete the bonding wire, you will still see continuity between your tank and the hull, due to the mounting bolts of the outboard. It is next to impossible to isolate the outboard negative side from an aluminum hull, so unless you're willing to remove your outboard, you can expect to see a ground path.

HRG

Yes, you will see continuity but it's not a return path- normally. But by tying in the negative post you now make it a return path and that's not good. The dual grounds- motor and hull tied into negative is what is causing the corrosion. The hull is never to be used as return path or it will be sacrificed.

[bladpart]

Originally Posted by Hot Runr Guy

the need for the bonding wire between the fuel fill and the tank depends on whether you have a metallic fuel fill (bonding required) or a completely plastic one (bonding not required).

I'll bet you a case of beer that even if you delete the bonding wire, you will still see continuity between your tank and the hull, due to the mounting bolts of the outboard. It is next to impossible to isolate the outboard negative side from an aluminum hull, so unless you're willing to remove your outboard, you can expect to see a ground path.

HRG

It's a metal fuel fill so the bonding wire should be necessary.

That's a terrible bet though . Of course there'd be a path to the hull if the +/- cables for the motor were connected to the battery. You're definitely correct that we would still see a ground path to hull through the outboard. That is expected. With the motor's negative cable connected to the battery, this would create a path to the hull through the motor through the transom bolts. That said, this path to the hull would provide a higher resistance path for accessories than the negative terminal of the battery itself or the sacrificial anodes on the motor, and why it would not be a problem as far as electrolytic corrosion is concerned. The motor also has a separate grounding wire that connects to a couple of the motor specific gauges on the console. Anyway, my mistake, I should've mentioned that the motor's +/- cables aren't connected, so they're not part of any of the continuity or resistance measurements being taken.

So, forgetting the motor for a second (disconnect the + / - motor cables from the battery), I'm concerned about how this bonding wire is connected directly to the hull without the motor connected. If I disconnect the green wire from the sender (other end attached to the metal filler) and test for continuity to the hull, it's 0.1 Ohms, it's a direct connection. Is it supposed to be like that? If so, why the bonding wire at all? It's clear in that case that the metal fuel filler is making contact with the aluminum hull already without the bonding wire. And I think it's a problem to have this direct connection to hull because when I hook up the fuel sender's return wire to the battery, now all my accessories are going straight to the hull through the bonding wire when they should not normally have any continuity to hull (because the motor is disconnected).

I guess where I'm going with this is I'm curious if the metal filler should be isolated from the hull (rubber gasket or something), and if the bonding wire should instead be taking a path to the negative battery terminal (and making something like a 150-200 Ohm connection to hull through the motor/transom when I hook it up), instead of a direct path to the hull.

[Hot Runr Guy]

Since the purpose of the bonding wire is to provide a connection between the filler neck and the tank, could the green bonding wire be moved over to one of the other tank locations, and not share the ground path that the tank level sensor needs?

Maybe a call to Moeller or Lund is in order? Or, replace the metallic fuel fill with an all-plastic one?

HRG

[bladpart]

Originally Posted by Hot Runr Guy

Since the purpose of the bonding wire is to provide a connection between the filler neck and the tank, could the green bonding wire be moved over to one of the other tank locations, and not share the ground path that the tank level sensor needs?

Maybe a call to Moeller or Lund is in order? Or, replace the metallic fuel fill with an all-plastic one?

HRG

That's an interesting question. From what I can tell, the tank itself is plastic and only the fuel filler is metal. My understanding is that you'd want to run the bonding wire to the negative battery terminal (or the negative bus bar which ends up going to the negative battery terminal anyway). I'm sure that's why it was spliced to the same ring terminal as the sender (since the sender's black wire goes to the negative bus bar/battery terminal already). Not sure where else I'd connect it in that case. I could maybe run the bonding wire directly to the negative battery bus/terminal...but then we're just grounding all the accessories to hull again through that bonding wire.

I guess if the fuel filler needs a direct connection to hull somehow...it's clearly already making direct contact with the hull even without the bonding wire.

Knowing what I know now, man I wish I could check this out back in 1997 when the boat was new. But, eh 10 years old at the time. Not sure how slow electrolytic corrosion is on a freshwater lake but I imagine pin holes would've shown up in less than 20 years. So, maybe it's just not a problem, but then again, maybe something changed with the connection. Think you're right though. I'll have to see if I can straighten it out with a call to Moeller or (hah hah)...Lund.

[bladpart]

Originally Posted by ltrain

Yes, you will see continuity but it's not a return path- normally. But by tying in the negative post you now make it a return path and that's not good. The dual grounds- motor and hull tied into negative is what is causing the corrosion. The hull is never to be used as return path or it will be sacrificed.

Touching back on this. I'm curious why it was spliced into the ring terminal and connected to the fuel sender. Now I'm wondering if that was done at the factory or by someone else that worked on the boat. I'll have to ask my dad of anyone serviced the fuel system.

Now I know you said to just clip it earlier. In that case, is connecting the bonding wire directly to the hull somewhere a better idea here? We don't have a metal tank, so I can't ground to that. I'm more concerned about sparking while filling the tank. Guess I'm not sure if that concern is necessary if the filler is already grounded to the hull without the wire (which is why you said to clip it).

[Ltrain]

Originally Posted by bladpart

Touching back on this. I'm curious why it was spliced into the ring terminal and connected to the fuel sender. Now I'm wondering if that was done at the factory or by someone else that worked on the boat. I'll have to ask my dad of anyone serviced the fuel system.

Now I know you said to just clip it earlier. In that case, is connecting the bonding wire directly to the hull somewhere a better idea here? We don't have a metal tank, so I can't ground to that. I'm more concerned about sparking while filling the tank. Guess I'm not sure if that concern is necessary if the filler is already grounded to the hull without the wire (which is why you said to clip it).

The way I'm thinking is if it's grounded to hull already why run wire already, what does it achieve. I could understand if it's a fiberglass boat, then yes that green wire goes to the negative post.
But I may be off in my thinking, I do like what HRG said a couple posts up, move it off that shared connection or better yet replace with plastic version