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While doing a recent rewire I thought I would take a few shots and do a little write up showing what is involved in doing a rewire for an engine conversion. The vehicle in question is a G1 S2 wagon and the engine being fitted is an 04 WRX. This particular job is fairly involved, mainly due to the addition of a factory immobiliser and fuel pump control system as well as the engine wiring change.

The first step is to cut away the insulation from the harnesses and strip out the unwanted wiring.
On the vehicle harness the unwanted wiring is the original engine management wiring.
On the donor engine harness the body wiring is unwanted, you only want the engine management wiring to remain.

I'll start with the vehicle harness.
First you need to ID which plugs are engine related, there are 3 groups of engine plugs in the engine bay in this particular harness. Start at one group and start stripping the wiring back from there. When you encounter a body harness plug(that needs to stay) you then pull it away from the engine wiring. At this stage I would cut the group of engine plugs off the loom as removal of the plug is the best way to ID unwanted wiring.





As you travel along the harness cutting away insulation and removing the engine wiring you also tape up the remaining body harness wires to keep them tidy and seperated from the wiring to be discarded.

Eventually, after a lot of removal of wiring and insulation you will be approaching the ECU connectors. At this point you can cut the discarded wiring off at the plug, this removes material and avoids confusion later.
DO NOT CUT OFF THE ECU PLUGS. They are your point of reference for any ECU - Body harness wiring. This shot shows the portion of wiring that goes to the engine itself and that is now removed for good.



After you do this to all 3 groups of plugs you will end up with a harness that is a shadow of it's former self. It should be taped incrementally to maintain it's original layout and I also use markers to show where the firewall grommetts, anchor points and other points of interest are along the harness.
Here's how it looks at this stage. The ecu plugs are still present but now only house wires that are body harness related.



In many cases there is also other wiring that needs to be discarded, commonly air suspension, auto trans and in this case speed sensitive steering. To do this requires tracing of the wires back to there closest connector and removing it there. Tracing the wire back physically is important because they will often tee off to another part of the loom. If this is the case then the wire needs to stay and only be removed at the module plug.



Now that the body harness is stripped out and ready to accept it's new engine wiring you can throw it aside and start on stripping the new engine wiring from the other harness. Here's how they start.



The method here is similiar but the engine wiring is the prize rather than the body wiring.
Start at the engine plugs and start cutting away insulation, this time cutting off the body connectors. As you strip the dead wires leaving the engine management wiring you need to tape up the engine wiring to keep it grouped and avoid tangles.

Eventually you will end up with the ecu plugs and all the engine plugs grouped together. These will be held to the tangled mess of the leftover body harness by about 30 wires(in this case, varies according to complexity of ecu). These wires are the links between the body and ecu and are what needs to be joined once the two harnesses are overlayed. Chop them off and group them together.

Continued..

In the late model Aus delivered harnesses(post 99), you have to contend with some little extras in the form of and immobiliser system. This consists of a small module, a key switch, an aerial and a key mounted transpomder. All this has to be incorporated into the older vehicle for the engine to run.



Other add ons are an OBD2 connector, flash memory connector and, in post 01 turbos, a fuel pump control module. This adds quite a bit of complexity to the rewire.
Here's the handful of plugs.



Eventually the engine harness looks like this and is ready to be overlayed over the body harness.



At this time you need to arm yourself with information. Without the appropriate wiring diagrams you cannot successfully do this sort of job.
Here's what was necessary for this job. 04 Engine pinout, engine diagrams, immobiliser diagrams and a tired old 92 pinout.



Overlaying the two harnesses can be tricky. You need to pay attention to wiring lengths(so all the plugs reach to there original places and also position the ecu harness branch correctly so it will drop down under the AC evaporator(G1 ecu's are not positioned here, all other models are). Once you are satisfied everything is positoned right you can tape the two harnesses together.

Next step is to start connecting body harness wires. This is where the old ecu plugs come in. Using your pinout or diagram, identify at each ecu connector the pinout function that needs to be connected. Cut the wire from the old ecu connector and solder it to the equivalent wire on the new engine harness. Repeat until all the old ecu plugs are completely cut away.

At this point you may need to connect extra modules for the new ecu as mentioned earlier. Integrating these into the old body harness may require more use of the wiring diagrams for other parts of the harness.

Eventually you should end up with something like this. Ready for reinsulating.



And after reinsualting and fitting the plastic guides and protectors.



This is now ready to be plugged back into the car and will fire up as per factory. This particular harness only requires an immobiliser status LED and a dedicated fuel pump earth wire so the controller can operate correctly. The igniton barrell assembly also needs to be used.

Any questions?

just one

on the second photo there is red wire near a green one was wondering if...

seriously, that is some hardcore rewiring - full credit to you and all the best with the project

sven

that aint a project, thats his job.

http://www.amauto.com.au

very nice Al.

wow some interesting work going on in that workshop. just spent 20 minutes ogling the pics. esp the twin subi turbo VK. looks quality too.

that's great! cheers for posting ;D might be very helpful to me soon

just one question al,if so will the abs still work if fitted or can this be a seperate system.....ie wheel sensors and computer and pump,so on so on and still will i able to plug the subaru select monitour in and look at fualt wise....

Any system that was originally in the car will still operate as normal, only the engine management is changed. Conversely, I can also remove unwanted systems from the loom. Commonly the auto trans wiring and air suspension is removed on Gen 1's.

The loom pictured now has two select monitor plugs, one original and the OBD2 connector for the engine management. The original connector is for select monitor 1 and is used to check cruise control and climate control in this case.

If you are asking whether ABS can be retro fitted(your post is not very clear) then yes it could but you would be better to get an ABS equipped loom of the same age and just fitting that.

oh! that looks like a big job. so ok, dose the wiring in a 1997-1999 impreza RX (AWD) 1994cc 2L also need to be changed if i wanna transplant a ej20 turbo in?
an can i get the wiring done by pro's?

^ I believe you can send it to Al if you can't find someone local...

Great write up and read with interest... one question - how about if the original ecu is being replaced with an aftermarket? What happens to the body wiring?

omg! was any one hurt in that? (pritty bad)

thanx for the tip!

Nah I got lucky and it was just pride and a bit of blood. Could've been a lot worse if I had've been going quicker / went off the other side of the road...

i need to do a similar thing... i have a 98 forester and a 99 (pretty certain) forester GT front cut. anyone know someone in WA that can come out and do the wiring? lol

You can just swap the loom over in that case, it's fairly straightforward, just use everything from the halfcut.
Doug at STechnic can help you with this if you can't handle it yourself.

in reply to the ABS question - yes you can BUT make DAMN sure you keep the system intact. in my case I have a 96 BG5 Legacy GT ABS 2E system in my 88 wagon. it involved the same principles as the engine harness swap and in my case a fair bit of custom work for the rear sensors. if you are doing it with a halfcut then take all the hydraulics and electrics with it.

if you are using a similar car then its a case of swapping the lot over.