How to wire the fuel gauge - Cars & Trucks

That won't affect the fuel gauge. Different circuits, entirely. Any issue with the fuel gauge is between the gauge on the dash, a little wiring to the gas tank, and the sender unit inside the tank. In most cases, the problem turns out to be the sending unit inside the tank.

To check the gauge itself for working, you can ground the fuel gauge wire at the gas tank connector, and watch for movement on the gauge, with the key in ON. You take the connector off at the gas tank, find the wire for the fuel level sender (or gauge), and touch it to a good ground- a metal piece on the car frame. If gauge is good, the needle will move either to full or to empty, but you can see the needle move to a new point, when you (temporarily, only temporarily) ground the fuel gauge wire. The key in the switch must be in on. If this causes the needle to move, then the dash gauge is good, and the problem is the sender unit in the tank. This unit has a variable resistor, not too expensive. The fun is getting to it.

The power wire from the sending unit runs to the gauge. Since it is showing 3/4 all the time. It is a break in the wire or really high resistance. I would check resistance of the ground wire first. If it is good(less than 5.0 ohms), I would replace the power wire from the pump to the gauge. I assume the gauge goes to empty with the key off. If not the gauge is bad.

The fuel gauge is directly controlled by the fuel sending unit inside the fuel tank, it sends a ground return signal back to the fuel gauge. I am assuming of course that your fuel gauge is okay. To test your fuel gauge, connect the wire which goes to the fuel sending unit to chassis ground. Your fuel gauge should respond and indicate Full Tank. If not, there is a broken wire somewhere between your fuel gauge and the sending unit. Before connecting the wire that goes to the sending unit to ground, check it first with a DC Voltmeter, you should be able to read +12volts. Be sure that you turn your ignition switch to it's ON position.

Either the gauge itself, or the wire from gauge to tank, or the sending unit in the tank. Most of the time it is a problem with the sending unit.

They work like this: in the instrument cluster, a small voltage regulator sends low voltage through the gauge, into the wire to tank, and to the sending unit. The unit has a variable resistor that varies according to the fuel level, measured by the float arm attached to the unit. What it (the gauge) actually measures is resistance to ground-the current goes to a ground point after going through the variable resistor in the sending unit.

You can check if problem is the gauge or the sending unit by grounding the fuel gauge wire at the gas tank connector. Pull the electrical connector apart and locate the fuel gauge wire. Jumper that wire to ground on the frame while watching the fuel gauge needle for movement. DO NOT ground it for more than a split second, just touch to ground while someone watches the gauge. If the gauge needle moves at all (will probably go to full or empty), then the problem is the sending unit in the tank. The gauge is good, so is the wire from gauge to tank. I should mention that doing this test can possibly blow the meter (gauges) fuse in the fuse panel- why I said to do it just for a brief moment.

Of readings are inconsistent with known fuel levels, Ground (or connect to a tester light) the sender unit wire and watch if the gauge rises.

The repair manual for your year,make and model, will have the wiring diagram you'll need to re-wire the fuel gauge.

there is two things : fuel gauge and dash fuel gauge. The fuel gauge in tank rated to 0 to 90ohms.disconnect wire at the tank take a variable resistor connect it to wire .read the dash gauge if it move as you move the resistor. if ok fuel tank gauge is at fault

Ensure that all of the wire connections are clean, secure and corrosion-free.

2 Check your fuel gauge fuse if the gauge's indicator stays on empty when your turn on the ignition. If the fuse is good, join the sending unit connector to ground. Replace the sending unit if the gauge indictor moves to the full line.

3 Ground the terminal located on the back of the fuel gauge with a jumper wire if the indicator doesn't move. If it does move, consider replacing the wire between the fuel gauge and the sending unit. A poor ground is frequently responsible for fuel gauge problems.

4 Release the wire that connects to the fuel tank's sending unit. Confirm that there's no worn insulation that would permit wire contact to the body or frame. A fuel gauge reading of full generally indicates a problem with the tank unit, not the wiring.

Most of the time its is the sending unit in the fuel tank. The test for it is to use a variable resistor that is hooked up to the wiring at the fuel tank and watch the fuel gauge if the gauge works ok thats makes 100% sure its the sending unit. At 245 ohms the gauge should read full, 180 ohms for 3/4 full, 160 ohms for 1/2 tank, 100 ohms for 1/4 tank and 42 ohms for empty. The color of wires at the fuel tank is purple wire and black wire. You can also use fixed value resisters. If the fuel gauge the wires from the sending unit to computer then to gauge for bad connections, shorts, broken wire and bad grounds. If the wires test ok that only leaves insterrment cluster or computer which even most dealers can't test eather one but the insterment cluster would be a more common problem then the computer. But about 95% of the time it will be the fuel level sensor in the gas tank that causes the problem. Good luck.

What was the original problem? Most fuel gauge problems are either a bad fuel tank sending unit or a bad ground wire going between the sending unit and the frame of the car. The gauge and wiring can be easily tested using only a 12 volt test lamp, once you have access to the wiring at the fuel sending unit. This often requires draining the fuel tank and lowering it from the vehicle.
To test the gauge in the dash and it's related wiring, connect the 12 volt test light between the wire between the gauge and the sending unit (the one with power in it with the ignition on). Make the connection near the fuel tank sending unit. Connect the alligator clip on the test lamp to a known GOOD ground. The bulb in the lamp should glow dimly. The dash gauge should read somewhere between 1/4 to 3/4 of a tank of gas. (Varies with make and model) This will verify that the gauge is either good or bad.