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Discussion Starter · #1 ·
I had a fuel tank issues this weekend when I started the motor for the first time of the season. The anti-syphon valve on the top of the tank had corroded in half and the fuel line fell off. Fixed that but the top of the sending unit was badly corroded also so I bought a new one. The old sending unit had a red wire connected to the center post and a ground wire on the flange. There was also a black wire about the same length as the other 2 that was tie wrapped with them. The black wire had a female bayonet type connector that was connected to a short piece of the mating male connector, but not attached to anything. I couldn't see anything that it might have originally been connected to and the fuel gauge was working before I started working on the top of the tank. Any thoughts on where this black wire came from. Do some sending units require 3 wires? The replacement only needs 2 (red and ground).
 

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Most fuel tank sender wires are pink and blk. The pink wire is for the sending unit and black is for ground. On some metal tanks they will also utilize an additional grounding tab some where on the tank. They will ground at both the sender ground tab and the ground tab on the tank if it is metal. Some boat systems with metal tanks will have bonding grounds which are usually connected to the fuel fill and the grounding tab on the tank, bonding grounds are usually green in color.
 

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Discussion Starter · #3 ·
Thanks for the input. The gas tank is plastic (Pro-Line boat). The original ground wire on the flange was green. I will try to trace the green wire to see if it is just to ground the fuel fill line. If it is, I guess the black wire should go to the ground on the new sender? If not, I still don't know where the black should go.
 

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A note about the sending unit, If you are using a Mecury with Smartcraft and have the fuel level tied in DO NOT CONNECT THE SENDER TO GROUND!

The Smartcraft is designed to read the sender in what is called loop power, this mean the sender is in a loop to the smartcraft harness.

On boats that simply have a fuel gauge the gauge have power to it then it goes to the sender and then grounded, it measures the resistance in the sender to translate it to level.

The same principal is used on smartcraft but if you ground it you may damage the computer on the engine.

know this because I did it, when I upgraded to smartcraft the manual said to do it this way so I did then I started experiencing problems with idling and racing. After the mechanic looked at it several times he could not find the problem, a merc rep finally revealed it.

I was told I would have to pay for a new CPU, I fought it with Mercury and they finally agreed that this was of no fault of my own because the instructions indicated this.

I received a new cpu and the fuel level sender is connected properly.

You may want to make sure of this if you are using anything like this on your boat.
 

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Fish hawk said:
Thanks for the input. The gas tank is plastic (Pro-Line boat). The original ground wire on the flange was green. I will try to trace the green wire to see if it is just to ground the fuel fill line. If it is, I guess the black wire should go to the ground on the new sender? If not, I still don't know where the black should go.

Black is always ground, the Pink is from your gauge to your sender, the green I am not sure, maybe for something else, try looking at the wiring diagrams for your boat to find out.
 

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Discussion Starter · #6 ·
The boat does have a Mercury outboard but not Smartcraft. Pink wire was connected to old sender and green was connected to a ground screw on the old sender flange. Black looks like it was connected to something at one point but corroded off. There are no other components in the area that the black wire could reach.
 

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We if it has smartcraft and you want to use it make sure you connect it properly or you can fry the cpu.

It looks like the green was the ground and the black was ground for the tank.

You need to make sure the tank is grounded, this prevents static electricity buildup and a spark from ignighting the fuel when you fillup.

something like this


(+)>---/ switch|--|Gauge|---------Pink-------|Sender|----black----->(-)


or (+)>--/ switch|----|Gauge|----Pink-----|sender|----green---->(-)

Tank|-----------------------Black---------------------------->(-)


Also, there should be a wire from the fillup spout to ground as well, this may be the green wire but I would not know why they used green? This helps discharge Static Buildup when filling up as well.

|Spout|-----------|tank|------------->(-)

In any case you need to trace out where the wires goto and come from, like I said try to get the manuafacturers original wiring schematics, call them that may be able to help you. I got them from My 84 Grady Whit.
 
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