There should be a vacuum diagram of the emissions systems on a decal somewhere on your hood.

If they are plugging into the ECU to see whats going on you may need to get an O2 simulator for the 2nd O2 sensor if you don't have a functioning cat, the cats operational state is determined from feed back from the 2nd O2 sensor, I believe its suppose to give something like a constant .4-.5 volts when operating correctly.