55.2-59 Gas guage?

[svr]

I have an autometer guage set, the usual 4 small guages with the speedo in the middle. I got this from a previous owner on ebay discribed as used for mockup only so i really dont know which fuel guage is in the cluster. In my mind i just figured it was correct for a 0-30ohm sending unit like the pickup original would be so thats what i put in my tanknever considering the guage might be something different. Anyway when the tank was empty the guage read empty. I put 2-3 gallons of gas in the tank and it pegged the needle beyond full. I pulled the sender out of the tank and checked it with my ohm meter, all seems right 0 ohms when arm is down and near 30 when arm is up. As soon as the sender reads even just 1 ohm the guage jumps to peg the needle beyond full. Ok maybe my ground is not good enough, so i pulled a temp wire direct from the sender to the groung post on my battery, nothing changed. Went looking for volts on the guage, i have 13 volts on the ignition side of of the guage but only 10 comeing out of the guage to the sending unit. Played around all afternoon trying different things, didnt learn a thing. Sitting here this evening the thought hit me what if the guage is for a ford sending unit that works in reverse of a chevy sender, early fords up to about 86 or so have a sender that operates from 73-10ohms, if original guy was useing a mustang tank and sender i suppose that is possible. Cant get my mind wrapped around how to test this to know for sure. Any thoughts or ideas? Thanks