Power Supply Routing

The main relay provides power for the ECU, several engine sensors and triggers the fuel pump on both the STi and RS. 

STi main relay wires: pg. E/G(ST)-03

1. Backup power supply. Goes to ECU plug B135 pin B19 and B61->F44 fuse box. Common with 5 and 6. Also to fuel pump relay. Switch off 10-13v, Switch on 10-13V, Engine running 13-14V.
2. Only to ECU plug B137 D17. Other end of ECU backup power supply circuit.
3. Control unit power supply. ECU plug B135 pins B5 & B6. Goes to several valves and sensors and electric throttle relay. Switch off 0V, Switch on 10-13V, running 13-14V.
4. To front an rear O2 sensors (bulkhead connectors B3 & B18)
5. Connects to 1.
6. Connects to 1 after B61. Also to data link connector.

RS main relay wires: pg. 36 Wiring

1. Ground.
2. ECU B135 pin B19. “Self-shutoff” control.
3. Control unit power supply. ECU plug B136 pins C1 & C2. Same as STi 3.
4. To front and rear o2 sensors (engine connectors E24 & E25). Same as STi 4.
5. To pin To fuse box B61/F44 and ECU B136 pin C9 – Backup power supply. Same voltages as STi pin 1.
6. To pin 5

Pins 1 and 2 control the relay. The voltages are reversed between these pins on the
RS and STi and pin 1 on the RS goes to ground instead of back to the ECU.

STi relay pin 1 will tap RS ECU wire B136 pin C9 which goes to fuse box via B61/F44 and on to the positive battery terminal. This wire also goes to STi ECU plug B135 pin B19.

pin 2 will go to the STi harness -> ECU.
pin 3 to the STi harness -> sensors and stuff.
pin 4 to the STi harness -> Oxygen sensors
pins 5 & 6 connect with pin 1.

 So, I will use the STi main relay and leave all the wires intact except for pin 1. That will splice into the RS ECU wire B136 pin 9 (which also goes to STi ECU B135 pin 19).

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I’ve got every item from the remaining list except one of the O2 sensors and an old impreza ECU arrived today.

The big table…

Here’s the table I’ve been working from. This table maps every 2004 STi ECU wire to every RS ECU wire (except for the couple engine to elsewhere wires). This also includes which wires will be blended from the RS harness into the STi harness. There are a couple question marks, particularly about the main relay. I’m almost set on buying another 2000 RS ECU, pulling the plugs, and doing all the blending between the RS ECU plugs and the STi harness so I don’t have to cut anything in the RS.

2000 RS to 2004 STi ECU Table

Still goin’

I’ve removed every wire in the harness that doesn’t connect to the engine or the ECU. All but about two of the wires from the engine go directly to the ECU and those both go to the combination meter for water temperature and oil pressure warning light.

On to phase 2: 

 There are a lot of wires that come from the ECU but do not go to the engine. Most of them, I think, will be spliced with the RS wiring but there are some, like the fuel pump controller, that do not exist in the RS harness. My next step is to make a spreadsheet of every STI ECU pin and map it to every RS ECU pin. I’m debating buying another RS ECU, ripping out the connector, and building an adaptor like they make for Honda swaps. Since it only takes about 3 hours to pull out my RS engine it might make emissions a little simpler…

 About that, I have talked with the department of ecology on how emissions testing will work with a swapped engine. Contrary to what I’ve read on local forums (Seattle area) the car WILL NOT be tested as a 2004 STI but will need to pass 2000 RS standards. This is true even if all the OBD2 wiring and emissions systems are intact. I was told by a testing station operator and two people at the department of ecology that connecting the 2004 STI ECU to the testing equipment will register as tampering and automatically fail the test before it even starts. Fortunately, I have also been told I have the option requesting a “sniffer” test, but I will need to contact the Washington State Department of Ecology before hand. They will then notify the station manager of the situation and how to test my car.

Parts I still need (at least)

1. Fuel pump controller and wiring.
2. Front wiring harness – (might make my own)
3. Gaskets for VF-39 turbo.
4. BPV gasket.
5. STI 02 sensors.