The ECM wiring is left intact, I just repin the wiring into the plugs. The Fiero harness is no left fully intact though. I cut the EGR Vacuum solenoid completely off and cut the connector. Those wires then get used for electric fan, knock sensor and other connections that need to be made. I also add in the digital EGR wiring to the harness. Generally, once the swap is done, no one would want to swap it back. The 7730 ECMs are more reliable, cheaper to replace and easier to service. I suppose if you wanted to switch it back it could be done without much trouble.