New fuel tanks - Grounding Question

[Germanmattlanta]

I replaced both the main and aux tanks a few months ago and I am now getting around to wiring them. I have a pink, a pink/white, and two black wires coming to the tanks. I also have two black wires that are attached to the fuel fill (one main one aux). My factory manual says pink wire is for the main tank and pink/white is for the aux tank.

I am confused which black wires go to the fuel senders and which are possibly the grounding wires. I am also wondering of I have accidentially pulled some wires into the abyss when installing new fuel and vent lines

Any help is greatly appreciated

 

[DennisG01]

Correct - pink is the standard color for the sender wire... and Pw/W would be for a secondary tank.

All grounds are connected together in the system... "ground". Which means it doesn't really matter.

BUT... you could ohm each black wire to the fuel fills to see which wire is connected to it. And/or ohm each to a known good ground or battery to see what wires are already grounded.

 

[Germanmattlanta]

Thank you! I made some pictures and have some questions. I’ll add them tomorrow!

 

[Hookup1]

This is 1997 268 Islander main tank wiring but should help. Ground wires are green. The wires to the boat run thru the flex cable attached to the fuel fill. They connect to a 2-pin auto/traller connector and the tank ground wire. The sending unit has the mating connector attached.

You have black ground wires. As Dennis said - "ohm each to a known good ground or battery".

 

[SkunkBoat]

normally the original gounding wires would be green not black.
The difference is that the green "grounding" wires are not intended to normally carry current.
Black "return" or "negative" wires are part of a circuit.
You should not use green wires as a negative circuit connection. However, gauge circuits tend to ignore this rule and use the tank ground as the gauge return.


Also, the newer KUS sending units use a black & white wire (or black & pink). The white(pink) is the negative and goes to a grounding point, the black goes to the gauge (your pink or pink/white)
It can be very confusing....

 

[Germanmattlanta]

I appreciate everyone's response and your patience with my lack of knowledge. I am attaching some pictures for reference. Starting at the fuel fill I have a black wire that is connected to the fill and the other is torn off. At the tank I have 2 black wires and one pink, and one pink/white coming through the stringer from the helm area. The new Wema fuel senders have pink and black wires. I understand the pink wire goes to the main tank fuel sender and the pink/white goes to the aux fuel sender.

This leaves me with the two black wires coming through the stringer from the helm. Are these the black wires that I connect to the black wires of the main and aux fuel sending units? If so, I have no cable left that could go to the grounding studs on the tanks.

I am also unsure how the two black wires at the fuel fill are related to this. Are they the same two black wires that come through the stringers from the helm area or do they go to some other central ground location (or is the fuel fill the actual ground)

My boat is a 1994 Gulfstream 232

Once again, thank you very much for everyones help!

 

[SkunkBoat]

The Green (or black) wires on the fuel fills should go to the ground tabs on the tank(s). there should be a Green (or Black)wire between the tanks and then from the tanks to the Neg of the batteries.
All of this is "grounding" to keep the fills and tanks at the same "ground" potential. technically, these wires never carry current . You should not use these as an attachment point for a negative of any circuit.
Using Green wire is a good indicator to prevent someone from confusing it with a Black "negative" wire.
Do they go to the same place? YES. But they are not the same function. Would a circuit work if you use the tank as a negative bus? Yes. but it would be wrong.
It could very likely cause gauge reading problems when you are using the circuit that uses the tank as a return.
Black return wires should always go to a Negative terminal bus or Neg battery terminal.


Do you have one fuel gauge and a fuel gauge switch? or two gauges? or a connection to a CL7 or other display?
The pink and pink/white are coming from those gauge connections. There should be a Black (or two) also, for the return of the circuit.
You need to find these connections. They will go to the sending units. As I said before, be careful because sometimes the WEMA(KUS) wire colors are reverse of what would seem logical.
Read the instructions for the sender.

Many sender circuits use the tank ground as the return and don't run a black wire back to the gauge connecction. Its not ideal but thats how they did it.

 

[Germanmattlanta]

@SkunkBoat thank you for the detailed write up, super helpful. I have ONE fuel gauge for TWO (main and aux) tanks and believe there is a small toggle switch that switches between the tanks (new to the boat). How would the negatives (black) of the two senders be wired with one gauge? Are the pink, pink/white and two black (negatives) coming from the fuel gauge?

I will rewire the ground wires in green. From the fuel fills to the tank tabs, connect the tank ground tabs, and then to battery terminal in the aft of the boat. Would I directly go to the battery negative terminal? I have a two battery setup with two battery selector switches. Does it matter if it is wired to the house or starter battery or do I go into the selector switch(es)?

What gauge wire would you use?

 

[SkunkBoat]

They will go to the switch. The switch is choosing whether the gauge connects to pink or to pink/white on the "S" sender pin
The blacks probably connect together to the negative/ground connection of the gauge or to a common negative bus for the dash.

Often the power to the + or "I" pin comes from the ignition keyed power (usually yellow).

Google fuel gauge wiring. lots of diagrams out there.