INTERMITTENT IGNITION ISSUE

Factory 1969 power scheme looks like this
upload_2019-9-27_12-47-7-png-png.png
I'd probably check inside the distributor cap for carbon tracks etc. Then the connections at the coil, then at the ballast, regulator and firewall. Might look at some spark plugs and the wires too if you think that ignition is a possible issue.