starting when releasing key

my 67 GT "decoy" sometimes will not start until releasing key. It has 78 318 with mopar electronic distributor and stock ecu, msd blaster coil with 4 pin ballast. After around 9,000 mi of driving this has popped up. Most of time it starts right up but occasionally if it winds for 5 seconds and don't start it will then start when releasing key. Replaced ballast but didn't fix it. Ohms check right and brown wire looks ok and connections. Wondering if maybe switch. Any suggestions, thanks Joe