fuel guage problem

I'm building a '86 wagon, converting the sheetmetal over to a '93 LX... The fuel guage is up past the full mark( the original '86) I thought it was the cluster and changed it only to have it go to the same place past full..lol I have the MT5 cluster with tach. Any one have a solution to this problem? All fuses have been changed and there are no cut wires in the harness.. The wagon seemed to be well maintained. I bought it at an estate sale and got some history, but can't figure the fuel guage....Help please?