check the circuit board where the light sockets twist on they may not look dirty but can definately cause that issue. i had it happen to me.take some steel wool and clean it.i did mine and everything worked perfect.
IT WAS A 9 YEAR CONCOURS RESTORATION.I WANT TO KEEP IT ORIGINAL AND THE PERTRONIX IS MORE RELIABLE.I HAVE INSTALLED THESE ON FRIENDS AND CUSTOMERS CARS NEVER HAD A FAILURE.WITH IT I CAN KEEP MY ORIGINAL DIST.
can anyone advise me as to which pertronix conversion kit for my 70 340 swinger dual point dist.seems to be alot of confusion with these kits. thanks jim