Backwards Fuel Guage

[anchors]

Upon purchase of my "71" the seller pointed out that the fuel guage reads backwards. He said he must have reversed the wires while reassembling the guage cluster. After removing the cluster to fix this I found the two wire plastic clip can only go on the guage one way and cannot be reversed. I would be gratefull for any thoughts on what to do next

 

[6880 Mike]

Is there a wiring diagram in the 71 assembly instruction manual (AIM)? Sounds like the wires in the terminal could be backwards. Check the color codes.

 

[LLC5]

Upon purchase of my "71" the seller pointed out that the fuel guage reads backwards. He said he must have reversed the wires while reassembling the guage cluster. After removing the cluster to fix this I found the two wire plastic clip can only go on the guage one way and cannot be reversed. I would be gratefull for any thoughts on what to do next

Does it move completely backwards form empty to full (a complete sweep from a known full tank to a known empty tank), or is the gauge staying on empty with a known full tank?

 

[anchors]

backwards fuel guage

the guage will swing its full arc, reading empty when full and moving toward full as the fuel is consumed stopping at full when the tank is empty. thanks.

 

[anchors]

color codes at guage are correct, not sure about a terminal, I think the wires go directly to the sending unit on the tank. thanks

 

[TimAT]

Just a single wire at the tank unit. Sounds like the terminals (wires) are reversed at the gauge. If the PO had the cluster apart, he may have flipped the connector on the back of the gauge- plug would still go on one way only, but with the wrong polarity.

 

[anchors]

I removed the connector and used jumper wires to reverse the leads, the guage needle went to the 3 o clock position and stayed there. Strange! thanks.

 

[TimAT]

Quick and dirty test- used it on all GM oil/temp/fuel gauges in my dealer days. Take a 12v testlight and install it in place of the sender, (unplug the sender, stick the probe into the terminal and ground the clip), turn the key on and the gauge should go to around 1/2 scale and the bulb should glow.

IT's also possible the PO tweaked the needle on the gauge and it's 180* out. Not real likely, but possible.

Going to 3 o'clock, sounds like the sender. With the jumpers installed, pull the plug on the sender and see where it goes.

 

[bagger]

When I replaced my center gauges a couple years ago I reinstalled the new ones with the resistor that was on the originals when I pulled them out and had the problem of the fuel gauge and temp gauge reading way off like the problem your having. Come to find out, the new gauges had a built-in resistor and the original resistor that mounted on the posts on the back side of the gauges weren't needed. I removed them and my gauges worked normal. Might want to ask the PO if he changed out the gauges with modern and if he did, did he re-install the original resistor back on them. Just another direction you might want to check.

 

[anchors]

thanks for all the tips, I'll give them all a shot and hope for the best