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.