Funky fuel guage after guage cluster swap

[Bounty Hunter]

My fuel guage is reading in reverse, from E to F as I drive (I wish it were true, but yes, I'm burning gas not gaining any). Would this be a simple fix by reversing the two leads from the sending unit (the two opposite the ground)?

 

I run an '88 4.0L shortbed and swapped in a fuel sending unit from a '91 2.5L longbed (same part number). I then swapped in the full-guage guage cluster in place of the idiot light cluster. I don't remember which direction the old fuel guage swept, but I'm pretty sure it worked correctly.

 

Anybody else experience anything like this?

[ROADLESS]

About the only thing i can think of is the ground. Theres also a screw on the back of the gauges circuit board labled 'FU'. Is this another fuel ground, try see if its making good contact. Thats all i can come up with :???: .

[Bounty Hunter]

I can't imagine it being the ground, as it appears to be working fine other than sweeping backwards.

[Pete M]

In 91 the gas gauge was reversed. Or was it the fuel pump? I don't know for sure, but the change happened in 91 and that's why your needle is reversed.

[Bounty Hunter]

The only thing I have '91 or newer is the fuel pump. Think i could reverse the leads or am I FUBAR'd until I get a different fuel sending unit?

[Pete M]

Then it must have been the entire sending cuircut that was switched. Not sure if swapping wires would fix it or kill it. :???:

[Bounty Hunter]

I was thinking there were two wire leads from the sending unit, not counting the ground clipped to the outside of the sending unit. If I can find out what signals the leads send, I may be able to switch them and straighten this thing out.