Removing ECU Harness Through Firewall
 

So Im in the process of pulling out the stock wiring harness to replace it with the one from my Megasquirt setup. Im running into some problems pulling the harness out through the firewall though. Does anyone know any tips/tricks to help speed this up or aid in any way?

You just wiggle it through from the outside.

There are 2 plugs under there that are NOT plugged into the ECU though....make sure they are unplugged!

there are two connectors (on s5 at least) that are up out of sight. Those along with the two ECU connectors (and maybe a ground) should be it. If you've undone all of those, you just need to get small hands to help guide and keep from hanging up on things. usually pulling the harness is not an issue.

*remember, the wiper harness is in the engine harness, so that will need to be cut out and reconnected. It is easy as well.

remove blower motor

^What he said, those 2 plugs that don't plug into the ECU are a PITA, especially if you didn't know they are there to begin with. I replaced my old crispy stock harness with a brand new one, so I was expecting those plugs, but it's still not easy to get to and physically unplug those suckers without little monkey hands. One tip that helped me out was I removed the glove box (door + insides, easy to do), and the lower dash trim where the dash speaker is. This was on an S5.

Like the others said there are some wires that don't go to the ECU (front wiper).

I pulled my wiring through the firewall into the car instead of out into the engine bay. I undid all the wire dressing and slipped it through, piece-by-piece, the grommet. I then pulled everything through the firewall. It was a PITA to pull all the connectors through the grommet but I accomplished it without destroying or cutting anything.

Yeah I got my 12yo nephew up under the dash and had him unplug those two connectors for me. After that it was all pretty simple. Just a few quick pulls and it all came out no problem. Now the fun stuff starts tomorrow and I get to wire in the MS harness.