MY93 - 96 ECU Pin-out & Apexi Fitting
 

The following images provide the Pin-Out for the 4-Connector MY93 to 96 ECU for the Subaru Impreza WRX/STI/UK

For fitting an Apexi PFC into a MY93 to 96 Impreza Turbo UK model no wires require moving or swapping.
The Apexi PFC will be Plug'N'Play (ignore my scribble below which was for select-monitor data mining).

However, WRX/STi/UK will be limited to 1.1bar boost due to the limitation of the MAP sensor hardware fitted to these models (injector and 'slanty' intercooler will also have performance limitations above 1.1bar).
To run in excess of 1.1bar it is required to fit an after market boost controller Apexi-AVCR (or similar), larger injectors and a higher surface area intercooler

http://img.photobucket.com/albums/v9...psuhhzchls.jpg

http://img.photobucket.com/albums/v9...psmdcshqcd.jpg

A little info here regarding fitting of the later Map Sensor : http://www.scoobynet.com/lighting-an...or-wiring.html

Note : When fitting this to an MY93-96 the boost target specified by your Apexi PFC will not align with the boost level reached. This is due to the different scaling voltage of the newer MAP sensor. You will need to calibrate the PFC with your external boost gauge.

It is possible to re-calibrate the scaling on a MY93-96 OEM ECU for the newer MAP sensor but only when fitting an ESL Live Daughterboard inside the ECU.

Engine Rpm Signal
(if wiring in Apexi S-AVC or external rpm/tacho)
Connector B96 Pin 16.
This is the larger of the 2 middle connectors with the wire to tap into on the bottom row (see above images).
Keying of the yellow connector should be checked to ensure you have the correct orientation (the large central key/tab on the connector is slightly offset).

The wire/connection you require will be either the bottom 'left' or bottom 'right' depending on orientation.
Unfortunately I can't be any clearer than that without an ECU/Loom infront of me as I can't recall if the image above is based on the ECU connector or the Connector on the end of the loom (as you look at it), as this obviously gives a mirrored view.

I have a feeling the MY93-96 ECU is represented one way and the MY97-98 or MY99-00 are represented the other, from a datasheet perspective (something I seem to recall I stumbled over before)