Not getting 12 volts to coil

71 Duster with 340. Electronic mopar ignition single ballast resistor. Engine tries to start but can't. More like sputters. Only getting 8 volts at + coil terminal when cranking/start. I found that I can get 12 volts to the + coil when I disconnect the wire connected to the negative coil terminal. The one that goes to the ecu. Also get 12 volts to the + coil if I disconnect or un ground the ecu unit. All readings when the engine is start/cranking. My problem is I don't know what these results mean? I have tried 2 different ecu boxes. My original chrome ecu box and a new hirev 7500 ecu. I also jumped the ballast. Same results. Thanks in advance for any advice.