I understand that it will have to be undone when the z6 goes back in., what I'm trying to get my head around is the wiring for the car it self i.e. the air condition sense,the ignition, ecu power, code light. Do I need to modify these if I'm just changing the engine. Let me see if I can clear up a few things. I have an EJ1 with D16z6 sohc v-tec with a p91 ecu. All of this is stock. I want to replace the z6 with a d15b sohc vtec-e with a p84 ecu in which I have the harness for but the harness has a few cut wires. Do I just search for the wires on the EJ1 and connect? Is it that simple?