[suntsu]

The sending unit is located in the fuel tank of the car. It consists of a float, usually made of foam, connected to a thin, metal rod. The end of the rod is mounted to a variable resistor. A resistor is an electrical device that resists the flow of electricity. The more resistance there is, the less current will flow. In a fuel tank, the variable resistor consists of a strip of resistive material connected on one side to the ground. A wiper connected to the gauge slides along this strip of material, conducting the current from the gauge to the resistor. If the wiper is close to the grounded side of the strip, there is less resistive material in the path of the current, so the resistance is small. If the wiper is at the other end of the strip, there is more resistive material in the current's path, so the resistance is large.

[greigmare64]

Something similar can happen when the float nears the bottom of the tank. Often, the range of motion does not extend to the very bottom, so the float can reach the bottom of its travel while there is still fuel in the tank. This is why, on most cars, the needle goes below empty and eventually stops moving while there is still gas left in the tank. here

[hanalin]

When the float is near the top of the tank, the wiper on the variable resistor rests close to the grounded (negative) side, which means that the resistance is small and a relatively large amount of current passes through the sending unit back to the fuel gauge. As the level in the tank drops, the float sinks, the wiper moves, the resistance increases and the amount of current sent back to the gauge decreases.

[den]

If that's the case, by your numbers, if I hook a voltmeter across S and (-) with key on, the voltage at empty should be about 7x the voltage on a full tank. Key off, an ohmmeter across the same terminals would give me the resistances listed, correct? here

[tenbagger]

Moderators: Since the question of how to properly wire a fuel gauge comes up so frequently, how about creating a sticky with this image? more

[humble]

So, I would think that I'm sending 12v to the sender wire, and the gauge is acting as a voltmeter, measuring V between the S wire and the gauge's ground. Is this correct? Here's a pic of what my simple mind thinks is going on.

[enoxice]

1) +12 volts on the "I" terminal? Yes or No. Yes = go to 2. No = fix it.
2) Solid ground on the "-" terminal? Yes = go to 3. No = fix it.
3) Short the "S" terminal to ground or "-" terminal. Gauge peg full? Yes = gauge is good. No = gauge is bad. Replace it.
4) If gauge is good, is there a good ground at shell of sender and battery ground? Yes = go to 5. No = fix it.
5) Short sender to ground (at the tank). Gauge peg to full? Yes = sender wire ok. No = fix sender wire.
6) If sender wire is ok, disconnect it at the sender. Measure resistance from sender terminal to ground. tank full = 33 ohms. tank empty = 240 ohms, half full = 109 ohms.
Readings roughly correct? Yes = system should be functional. No = replace sender. [links]

[kingandrew]

Re: How does the fuel gauge work?

[suckless]

Slip the female blade terminal of the stranded copper wire onto the "L" blade terminal of the fuel gauge. Remove the blade terminal for the instrument light of the instrument nearest the fuel gauge. Slip the stripped end of the stranded copper wire from the "L" terminal of the new fuel gauge into the female blade terminal for the instrument light for that existing instrument. Replace the female blade terminal on the blade terminal for the instrument light of the instrument next to the fuel gauge. This is called "daisy-chaining" the instruments. here

[narisseproe]

Disconnect your boat's battery. Look at the back of the gauge. There are four male blade terminals, one for the lights (marked "L"), one for the power (marked "I"), one for the ground (marked "-") and one for the wire from the fuel tank sender (marked "S") more

[midnightmagic]

Installing a new fuel gauge may not seem like a cause for celebration, but if you install and wire it yourself, you've saved enough money to throw a couple of very good steaks on the grill. Wiring a fuel gauge is much the same as wiring any other gauge on your boat: one wire comes from the ignition to the instrument, one wire comes from the sensor to the instrument, one wire comes to the instrument light and one wire from the instrument goes to the boat's common ground. The wires may follow a seemingly unusual path, but the system works.

[alanahbing142]

Daisy-chain the "I" wire of the fuel gauge to the power terminal of the instrument next to the fuel gauge. Daisy-chain the "-" wire to the ground wire--which may be also be marked "-" or "GND"--of the instrument next to the fuel gauge. [links]

[Cruzz]

Pull the wire from the fuel sender up through your boat's dash. Slip the female blade connector on the wire from the fuel sender onto the "S" terminal of the fuel tank gauge. Install the newly wired fuel gauge in your boat's dashboard.

[JohnVChampion]

If you are on a personal connection, like at home, you can run an anti-virus scan on your device to make sure it is not infected with malware. more

[momc4312]

Another way to prevent getting this page in the future is to use Privacy Pass. You may need to download version 2.0 now from the Chrome Web Store. [links]

[kiav]

If you are at an office or shared network, you can ask the network administrator to run a scan across the network looking for misconfigured or infected devices. here

[aaaxxx]

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