car dies when it gets warm

Hello,
I have an electrical issue that just started happening. It's a 318 in a 73 Swinger with stock electronic ignition. It's the 5 pin ecu and 4 post ballast resistor.
The car starts up great when it's cold. After about 15 minutes of running the car just dies. When I try to start it back up, it doesn't get any spark. If I let the car sit for 5-6 hours it will start right back up.
All these problems seemed to start after I changed my distributor, thinking the distributor was the problem I put the old one back in and I still have the same problem.
I've changed the ballast resistor, swapped ecu's and have tried a different coil. I believe my wires are good, I put in an Evans engine harness a few months back.
Any ideas? I just bought a multi-meter, what should I test?