4 pin ECU doesn't work. Old 5 pin does.

Since I'm not the only one, I figured I would state the problem succinctly, and put it out there for the experts.

Have tried several different 4 pin ECU's. And two distributors. Same result's. Nothing. Old 5 pin ECU cranks and run's the engine fine. For both distributors. New 4 pin won't. Swapped coil's also. Same result's.

For discussion sake, let's assume we have a good 4 pin ECU, coil, distributor. With old factory electronic ignition wiring.

Any idea's? Pin's 4 & 5 swapped? Bad connection's? Let's brainstorm. Thanks!!!