new fuel sending unit working backwards?? Little help please

[bill mason]

On my Allison the fuel sending unit stopped working. It had three wires coming out of sending unit. Got a new sending unit (this one only had two wires)?? Installed and it works except it reads full when tank is empty. Any thoughts. Thanks in advance for any input guys.

Stay healthy have fun

[265mercman]

you need a hot wire to gauge 12+volts.. then need 12+volts at sending unit and a ground at gauge and ground at gauge must go to the sending unit... the center of sending unit Is the 12+volt and the outside one is the ground

[H2Okie]

did you try reversing the two wires

[H2OPERF]

You prob have a european sender or gage they use opposite values for full empty, us is 240 ohms empty and 33 full... 3 wire would have been a capactance type

[SS Minnow]

Just turn the gauge upside down.

[perfmarine1]

you need a hot wire to gauge 12+volts.. then need 12+volts at sending unit and a ground at gauge and ground at gauge must go to the sending unit... the center of sending unit Is the 12+volt and the outside one is the ground

You do not want 12 volts at the sending unit unless you want to fire. Should just have a sending unit wire from gauge and two grounds

[gotboostedvr6]

Turn boat upside down.

[H2OPERF]

There are capacitance type 3 wire units that use 12v at the sender...they are tube type without a float, the tube type with a float normally only have 2 wires and dont typically ground to the tank like the old school wiper resistor ones...

[H2Okie]

Any analog gauge driven by a DC millivolt or milliamp signal will be driven "upscale " with current flow in one direction and "down scale " with the current flow reversed . The Polarity will determine which direction the pointer moves and magnitude of the signal will move the pointer travel from zero thru full scale .
A capacitive type device is going to convert the liquid level into a corresponding mv or ma signal to drive the meter . The simplest solution would be to find out from the fuel gauge manufacturer which sending unit(s) and wiring configuration to use with their gauge . It's only 2 or 3 wires how hard can it be?

[H2OPERF]

No ones arging how simple or hard it is just there are 1/2 and 3 wire senders and 2 different ohm to fuel level standards for marine gages depending on the which side of the pond you live on... so there are variables.

[H2Okie]

That's why I suggested talking to the manufacturer of the fuel gauge to find out type of sender(s) were compatible . They will have the answer right now .

[FUJIMO]

I like to stick with the old fashion swing arm senders. the centroid electronic senders require a hot wire to the sender. no thanks on a rough water boat. have "lots" of experience with the centroids.