Does polarity of fuel gauge wires matter?

[Noreg]

My fuel gauge didn't work, so I swaped the wires. Then the gauge showed the tank was full, and I was happy. But now it seems the gauge always shows full, which isn't exactly what I intended.

[Eli69]

It's just a variable resistor so it shouldn't matter. Can you see if the float is moving?

[phydeauxmutt]

As Eli69 says, it's just a variable resistor. The fact that it shows a full tank wired one way and nothing when wired the other way suggests that there is a short in the resistor. You can remove the sending unit from the EMPTY tank to inspect the windings. You can also connect an ohmmeter to the leads to verify smooth action when you move the float.

[2BRacing]

My fuel gauge didn't work, so I swaped the wires. Then the gauge showed the tank was full, and I was happy. But now it seems the gauge always shows full, which isn't exactly what I intended.

If you have the OEM workshop manual from the BassCliff site, there is a detailed section on testing and troubleshooting the fuel gauge and meter in the Electrical System section. Pages 262/454 to 266/454 in the PDF or actual page numbers in manual are 12-23 to 12-27. Note that the manual calls the section inside the revcounter the "meter" and the part inside the fuel tank the "gauge".

The tests describe how you determine if it is the meter or the gauge (float portion inside the fuel tank) that is defective. The fact that the needle of your fuel indicator now always shows full after you swapped the wires, shows that that part is working and your problem is at the float unit inside the fuel tank. Very often the problem is caused by a loose wire or poor contact at the variable resistor part of the float inside the fuel tank.

On the BassCliff site there is a "Fuel Gauge send unit repair" document by member Jethro. I have it in PDF version - cannot upload it here - send me a message if you cannot locate the document.

EDIT: The page numbers I quoted above are from the 850 manual.

[rphillips]

No electrician but... If wires hooked correctly & gauge shows one thing, then wires hook other way & gauge shows something different, that should answer if polarity of fuel gauge wires matter. If it didn't matter, gauge would read the same wired either way...I think.

[phydeauxmutt]

No electrician but... If wires hooked correctly & gauge shows one thing, then wires hook other way & gauge shows something different, that should answer if polarity of fuel gauge wires matter. If it didn't matter, gauge would read the same wired either way...I think.

Unless there is a problem with the wiring in the sending unit. If the winding of fine wires has broken and one of the loose ends is grounded, it will show as a full tank when the wires are connected in one direction. When the wires are connected in the other direction, the gauge only sees the open wire, therefore NO reading on the gauge.

Probably not a common occurance, but it is possible.