Distributir wiring

What engine? I thought all Mopars by 1990 had a Hall-effect distributor pickup, which has 3 wires, which I see in your photo. It is a better type of sensor since it has a "DC signal", i.e. you can turn the distributor as slow as you want and the signal will be the same level which you can read at your leisure on a DC multimeter.

The problem is that the HEI module is designed to work with a 2-wire "variable reluctance" sensor. You can read all about VR sensors on the megasquirt site since many there use the Ford EDIS crank tooth sensor (I put one on my 65 Dart). A VR sensor has an "AC signal", which you need an oscilloscope to see. It oscillates positive and negative about ground. Also, the signal is stronger at higher engine rpm. There might be a way to rig a Hall-effect sensor to work with an HEI module, but would require an engineer like me or a smart electronics technician. The first Mopar electronic distributors (1972 - 1982?) had a VR pickup, as did GM V-8 distributors thru 1995 (trucks) or 1993 (cars).