1970 2002tii Gas Gauge Stays At Full

The needle stays at full. I bought a new sending unit and it still reads full at all positions. When I disconnect the tan sending wire, it goes to empty (like it's supposed to). When I hook up a new VDO gauge, it reads 1/2 at empty and OVERFULL at the full position.

Is there a voltage limiter or regulator which lowers the voltage (or amperage) to the gauge that is shorted across?

Or is there another problem?