1973 Scamp won't start in start only in run. With a Twist....

Well troubleshooting by remote control "is hard" LOL

I guess all I can suggest is to go over the wiring carefully. One thing I'd suggest is to isolate the ignition from the rest of the wiring and jumper it to run. In other words separate it from both the "run" and the "bypass" circuits, IGN1 and ING2.

They carefully check both those sources WITH A LOAD applied, IE an old headlight or anything 12V you can find that will draw maybe 5A or so. Measure voltage in "run" and "start."

Is there any other added electrical wiring/ changes?

How about former damage, IE wires crossed / melted in the harness?

It might also be that happenchance is leading you down the wrong path. An intermittent/ poor connection in either the ECU connector or the distributor pickup connector can drive a guy nuts