The Engine Control Unit (ECU) from the older non-turbo car could not run the turbocharged engine from the STi. That meant we’d have to use the STi ECU. But the ECU and the engine use a specific wiring harness. We decided to just transplant the entire wiring harness from the STi and bring over as many parts as possible with it (like the instrument cluster).
We started by removing the mechanicals from both cars. The take-off parts from the older car were hauled over to a storage locker and sold. We recovered a little bit of cash that way, but factoring in the time and effort of moving parts around, not to mention storage space rent, we probably should have just announced “Free parts!” on the Internet forums and let people come and take them away.
The electrical system was more complex. We could wire up the STi ECU to the STi engine just fine, but the rest of the wiring harness had to plug in to parts on the car like the lights, power windows, door locks, and other little bits, and they were not wired the same as on the newer car.
We had to do a lot of cutting and splicing and sometimes had to get creative. The windshield wiper motor lives on the opposite side on the older car, so we had to extend those wires. The dome lamp has one wire on the older car, while the newer car has three wires. I think we just punted on that and did without a dome lamp. At one point we had the door locks and windows wired up, but window switches were operating the door locks and vice versa.
We did make our lives a little easier by using the STi gauge cluster. Actually, we transplanted most of the STi interior, including the entire dash and the center console. The dash did not bolt in directly – we custom-welded the dash support beneath it to make it fit.
Despite taking a lot of care, we had some casualties of the transplant process. The front windshield cracked, probably from the stresses of moving the chassis around all the time, and we had to buy a new one. We managed to damage the clock spring on the steering wheel somehow. Quite a few bolts broke off in the disassembly process and had to be replaced. I can’t count the number of small plastic parts and bits we had to order from Subaru to replace old, broken, or lost parts.
I did manage to stick to my promise not to modify the engine … almost. We did custom-make a cold-air intake for the car, and we installed a full exhaust system generously donated by our friends at TurboXS™.
Other suppliers kicked in parts for the car, including Kartboy (bushings, short shifter, end links), Prosport (gauges), Rota (wheels), and Seibon (carbon-fiber hood).