Is the "bigger red wire" supplying the ign switch with power from the bulkhead connector, on the passenger compartment side? Are all of the terminals you checked clean and such?
When I put the old Mopar Perf electronic ign conversion kit on my '67 Newport. When I first tried to start it and it did start, I repeated the start-turn key off-start process a few times. On the 5th try, nothing. Voltage was where it should have been in the appropriate amounts, but nothing to the ign switch.
So I started looking. Got a new starter relay as it was the original part, although it had voltage and I could jump the starter from there. New part, no change. Battery had enough volts in it, too.
Further notice was related to the battery terminal ends and posts. I could see a thin layer of grunge between them. Nothing major at all, just a very thin layer. I got a wire brush terminal end cleaner and cleaned the inside of the terminals and also the inner surface of the cable ends. They had plenty of voltage, too. BUT afterward, the car started as it should. NO problems after that.
This taught me that going by looks alone is not good enough. Possibly voltage can get through the grunge, but not amps? Or the heat from energy transfer through the grunge made it more current-resistive?
On another car, it would get an intermittent "failure mode" while driving. Took a good while to track that one down! When it would fail, I would lose about .3volts inside the ground cable. Cable was new and looked great externally, but apparently had something internal. New cable fixed that one. Again proving to me that cosmetics might not be a good judge of what's expected to be inside.
On still another car, my '80 Newport 360 2bbl, I put a new set of quality spark plug wires on it when I got it. About a year later, it developed an issue with it wanting to go into limp-in mode in the computer. I could detect it with a very slight additional shake at idle, but when throttle was applied, it really shook, but was not missing.
One day, I was in the drive-thru to get something to eat and I felt that additional shake. Confirmed when I move it off-idle. Being across town from my shop, I was scared to turn the car off, so I let it idle as I ate, and then plotted the best way to get back to my shop. The car would barely make 45mph in 2nd gear to get over the slight overpasses as such. Took over a quarter tank of gas to go about 15 miles. After I got the car inside the shop and parked it, then I turned it off. Let it sit overnight. Next day, it started up and ran smooth! So the search began, looking for lost grounds that would trigger the computer to go into limp-in mode. All major and minor grounds were found to ge good.
So i next decided to check the spark plugs. When I pulled the #1 plug boot off, the terminal part of the wire stayed on the spark plug. It never had been securely crimped to the wire, but it took a year for that to manifest itself. So I slid the boot down the wire, re-crimped the terminal securely to the wire, slid the boot back down to cover it, put it back onto the plug, and no problems since then.
Apparently that un-fired plug sent a voltage spike back to the computer and the computer went into limp-in mode. IF I had been brave enough to kill and re-start the motor, letting the computer "clear", things would have been fine.
Just some of my experiences with vehicular electricity issues.
Take care,
CBODY67
