"My understanding is that there is a ballast resistor involved"...I think the harness has resistance wiring built into it. I've never noticed a resistor on my car (71 LT-1).
There is information and wiring diagrams on the internet, but some of these are for a add on kit that GM sold.
I used a replacement board from these people, car starts and idles better then it did before (old board got smoked). Been several years with no problems.
https://www.lectriclimited.com/elect...x-module-87041