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

Ok I'm confused
Are you saying;
That when you return the key to run, from cranking, and while the engine is yet spinning, then it fires and runs?
Cuz that proves everything is normal on the blue-wire side; including the ECU and pick-up,etc. WHEN THE STARTER IS NOT CRANKING
And you have near-battery voltage at the coil, in RUN?
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And you say that in crank-mode you have 6.5volts at the coil positive?
And you have no ballast resistor?
Well that's not right;
It seems like;
1)either the starter is sucking up all the juice,or
2)there ain't enough juice to go around,or
3)there's a dam in the line between the battery and the coil, on the CRANK line,usually the brown wire; and since the starter relay works, I'd guess it would be between the ignition switch and the coil.

The easy test is to jumper from the battery to the coil +, and then hit crank. If it now starts and runs, then you have ruled out the first two possibilities.