Gas gauge not accurate/unresponsive to fuel level change

I have a 1973 Z and the fuel gauge is showing full, even though I emptied the tank and added only about 1 gal. This is a new fuel gauge sending unit in the tank, swapped in in the last year. It seemed like it started having this problem after I put in a Pertronix Ignitor starter, but that doesn't seem to make sense. Here is a pic of the wiring at the tank, and 2 pics from ballast area under the hood.