Help needed with MSD “No spark” mystery

[BartdeBruijn]

Not sure to put thread here or in engine build forum!?

Loosing my mind slowly……

History:
Good running 911T 1969 with CDI and Bosch distributor
After years perfect running intermittent ignition cut outs. Sometimes short, could restart sometimes towing back home.


CDI has high pitch noise etc. But as I wanted to rule out the old electronics I purchased a MSD 6A and blaster coil.

After installing MSD there was no spark at the test spark plug cilinder 1 connected to the distributor.

Findings & checks done
- When connecting spark plug directly to the coil lead and grounding the trigger wire (white) from the MSD if have many strong sparks.
- Checking my Bosch rotor with resistor turned out to have infinite/open resistance. Found stories about fried resistors.

Mounted original rebuild Marelli distributor with zero resistance between new rotor points.(coil wire input and cilinder position output)
- Same story, no spark from spark plug connected to distributor cil1.
- When checking the wire connected to the points from Marelli distributor with multi meter one reads the opening and closing of the points(zero and infinite resistance).
- When connecting the spark plug directly to the coil (to rule out rotor and cap of rebuild marelli) and connecting the white MSD trigger wire to the points wire(that measure open and closing) and rotating the crank 720 degrees to be sure that cil1 will go through compression TDC (to rule out some timing mismatch….no spark…..

So MSD fires when white wire is grounded and spark plug is directly connected to coil
Points open and close measured on wire that comes from points (the one that need to be connected to white MSD wire to trigger a spark
Though the points do give a ground (measured open and closing)the coil does not fire through the distributor cap - rotor - plug wire - spark plug route!

Help / advice would be highly apriciated!
Thanks,
Bart