Error code 43

I have a 1996 Plymouth Voyager with a 2.5L. It has been running very rough; misfiring, rough idling, and stalling. The trouble code I'm getting is 43 which means and interface problem, Ignition Coil Control Circuit problem, or an Ignition Coil One & Two Primary Circuit problem. I have changed the plugs, coil, and wires and still no luck. This is telling me that it must be the interface. Can any body tell me what that means? I think I'm now faced with having to trace the wiring back from the coil but have no idea how to go about it.

ANy help would be great

Turns out the error code was just trying to tell me that I had a bad plug. It must've been a dud from the factory.