Ignition:Sparks for moment, then nothing

[tx914]

74 2.0
Daily driver that has run great for years then all of a sudden died. Now it occasionally starts runs strong for 30 seconds then dies completely.

Troubleshooting:
Battery fully charged/car cranks strong
Getting fuel, just no spark
ground strap cleaned
Neg Battery cable checked
all relays on board checked
When engine cranked, I get a big fat spark from the coil for a few revolutions then nothing
Points clean and operate normally, you can see them work with the cap removed, electricity flows for the same amount of time as the coil
Cap clean, not cracked
Rotor like new
Alternator and dashboard operate normally, light goes out when it decides to run.
Cleaned and reseated just about every electrical connection

any help greatly appreciated, Thanks

[RandyLok]

Check/clean the ground wire connections on the engine harness. Particularly the group of white ones under/behind the plenum - I forget exactly where they bolt up.

[Rouser]

Try swapping coils ...

[tx914]

Tried swapping coils and cleaned/reattached white engine harness wires. no change.

[Dave at Pelican Parts]

How's the ground braid inside the distributor?

--DD

[Conrad W Peden]

Try with the Tach disconected.

[tx914]

The culprit: ground braid solder point in the distributor.

Thanks to DD for the insight.