HEI in a 396 that all of the sudden runs only on when cranking

I have tested power when key is in run mode and have 12 Volts out at the distributor. Changed module ran fine drove it for about half an hour and it is back doing the same thing. Thinking it's not the module but something else in the distrbutor. It is a large cap Chevy HEI, any ideas??  

i take it that this is in an car or truck that had points type ignition from the factory.

in point type wired cars... there is a wire from the ign switch... it changes to a resistor wire at the bulkhead connector...

at the original coil there was a second wire... that went to the R terminal on the starter... (left side of the solenoid)   what this wire was for is to supply the coil with full battery power only during cranking..  when the key is in the crank position.. it breaks the connection to the coil +  at the ignition switch...

i would check the wiring at the bulkhead...  and for power on the pink wire at the switch...

on hei's ... i usually pull the coil cover... and put a test light into the batt connector from the top...  ground the clip...    then turn the key on...  see if the test light lites up...... during different movements of the key... and during cranking...

while you have the coil cover off.. make sure that there is a ground strap that fits into the center connector of the 3 wire connector.. it grounds the black wire out of the coil...   completes the circuit back to the coil...   without this strap...  i have seen the coils explode with enough noise it sounded like a shot gun going off...


depending on the year of your car/truck.. you might want to replace the resistor wire from the bulkhead connector to the hei with regular automotive quality wire...   replacement terminals are sometimes available from the local parts stores... the resistor wire will be fiberglass covered..


hei's like full battery voltage... with the alternator working..  

I was working on a 1971 C10, the truck was converted to HEI and ran fine for years then started doing the same thing. It turned out to be a bad ignition switch. It was the original, but before I dug through the wireing I would try running a wire straight from the battery to the + side of the coil. This would seperate the coil from the rest of the wireing, Also be sure all of the ground straps a clean and tight. What vehicle is this? I haven't had one lose power on the coil wire while starting