Does the black wire reach the solenoid male terminal at the top of solenoid. I imagine the engine harness for this option would have the power feed harness on it. The 71 service manual shows a DBL wire to the red bullet power feed coming from a #1 splice. Which is the splice in the J2 wire that feed ballast and VR wires. There might be a jumper to get the black wire to the terminal of the solenoid for idle.