both Cab and SCG have excellent suggestions.
I will mention a few others that were "FUN" to find.
1. Freshly restored 72 Cuda with all new harnesses. it would die every time one closed the R door but start right back up and run fine until the door was closed again. Problem : When the Connector for the control module was molded, one of the female terminals was to deep in the connector and BARELY touching the pin on the module. closing the door would open the connection and the motor would die. The reason i mention this is it was a potential HIGH RESISTANCE connection.
#2. Mis-wired ballast resistor when conversion was done. They had pulled the 12V signal for the Control module off the WRONG side of the ballast. Electronic components are finnicky. Sometime a 12v component will work at ~8 V and sometimes it won't. Why? numerous variables, temp, voltage, resistance and it's mood LOL
#3 Wire to pickup coil inside the distributor was broken internally. I assume it was from the vacuum advance moving and flexing the wire, BUT I have also found brand new wire with internal strands open inside the insulation. these can usually be detected by pulling opposite directions on the insulation. If a section seems weak or "stretchy" discard it.
#4 Bad crimps an on new harnesses. There are two parts to the crimp. The first crimps the copper wire. It should be tight with NO insulation inside the crimp. The second part is the strain relief which crimps on the insulation. it should be snug and prevent the insulation/wire from moving When inspecting flex the insulation where it enters the terminal. if it feels weak, it is likely breaking or broken internally.
#5 You've already replace d the ballast but i will mention it for others. The resistors will sometimes start to deteriorate internally causing intermittent issues like you experiencing
#6 Bad coil wire. They can be also broken internally or have had a bad connection on one end which has Burnt the conductor from arcing.
#7 as suggested make sure the male and female terminals fit snug for a good electrical connection.
#8 Any added terminals should be PULL tested to verify the integrity of the crimp.
#9 be aware that different terminals require different crimpers. Some are some what universal ( Home depot, harbor freight etc). Some should also be crimper a specific way. BUBBA doesn't adhere to theses ideas and believes a pair of pliers will work just fine or a hammer and punch on a battery lug
keep us posted
