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Fuel tank grounding

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realcaptron

Regular Contributor
So as I'm doing a new blower install, I discover the fuel fill ground wire corroded off and hanging. So I start exploring the tank grounding itself and see grounding tab on top of tank (aluminum) with ground wires disappearing into the spaghetti of wires into a bulkhead and no evidence of where they come out again. I test ground from tank to engine block, get no ground. Test block to hanging deck fill wire, still no ground. The wire goes to the tank ground tab. So if I run fresh ground wire to tank ground tab, do I ground it directly to battery negative, block, or bonding wire to transom anode?
 
Positive and Negative only to a 12 vdc system. (Ground is a term used in AC systems...... as in Earth Ground)

The wire to the fuel tank tab is the Negative for the fuel gauge system.
You may also see a bonding wire that runs to the metallic fuel fill fitting.

Try to avoid any direct battery connections, other than battery cables themselves.

All subsequent circuit Negatives can be connected to a common Negative termination point.
 
I think its better to refer to them as bonding wires .....the filler port should be bonding to the tank and the tank to the hull's bonding plate. If no bonding plate, I've seen the engine block as well as the strut used. and these wires are separate from the tank's sending unit return....
 
Thanks Mark and Rick. Understanding better now. This old boat does not have fuel gauges
While waiting for your responses, I discovered that the lead from tank tab to whatever it was once connected to (on BOTH starboard and port tanks) was mysteriously dangling disconnected with a ring terminal crimped on. Seems deliberately removed for some reason on both sides. The fill fittings are supposed to be bonded to the tank tab but those were rotted off. The leads with ring terminals have the right length to go to each block. When I ground to block with vise grip, and touch tank with multi tester I get very slight resistance, barely enough to move needle but something. So I'm guessing that intention was to ground (bond) to block, just don't know why left hanging by somebody at some point in time. Are you guys suggesting I bond that tank tab to anode plate rather than block?
 
if you have an anode plate, that would be the best destination; if no anode, the engine block is adequate......slight resistance in the bonding path is ok - the main purpose is to dissipate any static charge that shows up during filling.....
 
makomark said:
the law says the bonding path for the fuel system can have up to 100 ohms of resistance....
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I guess I'm really going to expose how ignorant I am on this. With multimeter set on 1000x ohm scale, when I have the tank grounded to block now the meter reads 2 on the ohm scale. When I remove that ground from the engine block and clip it to an anode bonding wire and them probe the block and the bonded terminal, it still reads 2 on the 1000x setting. Feeling really uneducated.
 
diver_dave said:
2000 Ohms? if so, too high. What meter, exactly? Just the leads together must read close to zero.
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Dave, forgive the typos. I'm voice typing right now. I don't know specifically which brand the multi tester is it's an older analog I put fresh batteries in it. But when I touch the two leads together it does not go to zero it almost gives me the same reading of 2000 as it is what I'm reading anything else. Tomorrow I'll buy a new tester and try again
 
it should have a zero adjust knob or dial.....set the range multiplier down to like 1x or 10x....clip the leads together.....zero meter.....then take reading.....some styles have the zero knob partially hidden in the case - similar to the volume or tuning knobs on an old transistor portable radio...
 
makomark said:
http://www.acehardware.com/product/...MI0YfVhLik2gIVkEsNCh2u2wQzEAQYBCABEgIxpvD_BwE

if the link works, there's a hidden red knob, on the LH side right below the meter's bezel -> zero knob

sorry - dup post.....
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Voice typing again. Yeah the meter I was using has a dial on the right hand side of it I turned it in both directions the needle tried to come down but would not come down to zero. I have another tester at home I'm going to take a look at it and see if I can get it 2-0 if so I'll try that tester tomorrow. You guys are great I appreciate all your help
 
realcaptron said:
Voice typing again. Yeah the meter I was using has a dial on the right hand side of it I turned it in both directions the needle tried to come down but would not come down to zero. I have another tester at home I'm going to take a look at it and see if I can get it 2-0 if so I'll try that tester tomorrow. You guys are great I appreciate all your help
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usually low battery causes this; sometimes bad contacts to test leads. spin them.
 
diver_dave said:
usually low battery causes this; sometimes bad contacts to test leads. spin them.
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Update to everyone helping on this . With significant effort and cutting some access hatches to get to the tank grounding tabs on both tanks, I found virtually all the terminals corroded off, thus no tank grounding of filler bonding was in place. Replaced all wires and terminals with new
Ran tank ground from tab to engine block and bond wire from fill fitting to tab. With new digital tester, resistance is 0 when touching probes together and pretty much remains 0 between block to tank and between fill fitting and tank
. Hopefully that's what I'm looking for.
 
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