So all the above pictures were only the prep for the wiring job. What I did was take one wire at a time that leads from the ECU and followed it to whichever plug it went to. After I found said plug I marked the number of the plug (OEM style numbering) and labelled the position of the wire in the plug and also a general note such as “to gauge cluster” or “ to fuel pump”. Doing this made the wiring job MUCH MUCH easier when it came down to start soldering. I would strongly suggest this as it’s hard to find some wires in the diagrams and you could spend many extra hours just searching for wires in the damn diagram books. Plus, on the 2002 WRX and 1999 RS the colors of the wires are mostly the same. Many times I marked a wire as going to the cruise unit or some other device, when I searched for the same wire on the RS it was the exact same colour and sometimes even in the same position. What I’m trying to say is take more time to prepare the harness and you won’t be sorry. My car started up the first time without any check engine lights or any problems what-so-ever. I listed all the positions of the wires in the car (1999RS and 2002WRX). So on the following pictures if I list something like B134-19 RS, this means that it is in plug B134, pin #19 on the RS. It’s really easy to figure out this system once you’re in there. The next pictures really don’t show much but pay more attention to the pin numbering instead.
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The first wire; AC Pressure Switch. B135-27 (RS) to A2 (WRX)
Both cut ends of the wire.
Leads to this plug which plugs into the side of the AC box.
Soldered wire.
Shrink wrapped wire (still AC Pressure Switch).
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Starter Switch. B135-28(RS) to A16(WRX). This is one of the few thick wires. Notice we got ahold of the sticky blue tape that Subaru uses and made the same type of connection they do along with soldering.
The electrical tape made that same connection look ugly but it's more to make sure it's protected.
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Test Mode Connector. B135-14(RS) to A14(WRX).
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Fuel Level Sensor. B136-28(RS) to B25(WRX).