Warm the car up for 2 minutes first. Open the EEC test cover under the hood. Take paper clip (big one) and unfold it and push one end into the SIG RTN pin and the other into the STI lead. Lay it down on a piece of cardboard or something to keep it from contacting the frame of the car. Get in and turn the key on and start the car. Sit back and let the test start. Within 5 seconds, push the brake pedal and let off and turn the wheel 1/2 turn and back. Wait for the single "goose" pulse and press the throttle all the way and let off. Then wait for codes.
If you have a Haynes manual, this is covered on page 6-5. It will read back stored codes first, then run codes. The timing is 1 sec between counts.. (e.g. flash-1secpause-flash would be a 2) 2 seconds between digits (e.g. flash- 1secpause-flash-2secpause-flash-1secpause-flash would be a 22). 4 seconds between sets of codes. A 1 is a pass code.
If you have no problems, 1, 1, 1, 1, 1 means everything is perfect. The middle 1 is a separator between the stored and run code sets.
The codes will be output twice and this takes a bit of practice to get them all.
Good luck.
Here's a diagram of the EEC test harness.