My Fuel Gauge Don't Work

[conman]

I did a body swap putting a 70 model body on my 72 model chasis. I put the fuel tank from the 72 and also the gauge cluster. Before the swap the gauge worked perfect. Now, the gauge reads almost a 1/4 turn low. I know the wire is not broken. The only difference is the wiring harness plug-in on the 70 body had a total of 11 contacts,( 6 on top, 5 on bottom) the 72 has a total of 12 ( 6 on top, 6 on bottom) I cant figure this one out.