[FourthGenHatch]

Take off the DX engine harness and put it on the Si/ZC means unplug all the plugs and wires off of the DX engine (same as LX engine by the way) and plug them onto the sensors and stuff onto the Si/ZC engine.

I'm not sure if you have to extend wires from going from DX > Si since they are SOHCs, but from DX > DOHC ZC I know I had to.

Plug side and harness side had do do when you cut a wire in half, the half of the wire stuck into the plug is the plug side, the half of the wire that goes to all the other bunch of wires is the harness side. I'm going to get a picture later on to better explain that.

And you do need new MPFI ECUs, it says that in my How-To.