I've been busy this weekend....... Once again, I found myself searching through dozens of threads about gauge installations, especially about the A/F meter, which was usually accompanied by ridicule and doubt, and really offered no help at all.
So I did it all myself, and although I'm a LONG time car buff..... I'm a newbie to the WRX world. I KNOW there's a lot of folks out there that need this info..... I needed it myself this morning, and couldn't find it. So I'm offering this up to any other newbies like me, that need the help. I bought a set of Autometer mechanical C2s... but I imagine most gauges are about the same. I ran the illumination wire on all 3 gauges to the ORANGE wire on the factory stereo harness, and the ground wire to the BLACK wire on the factory stereo harness... poof, I had light.
Really only one thread helped me...... because someone already created one, so far be it from me to tell you otherwise. Here's the directions on installing an oil pressure guage:
Now, this tutorial explains how to do it with an electrical gauge, but it works the same with a mechanical one. You will need a crows foot, and I recommend a 10 inch extension for your ratchet, and an allen-head socket. The plug is in there TIGHT,.... I have no idea how he was able to get it out of there with just an allen wrench.
My other advice? DON'T DO IT!!! This gauge was a PAIN IN THE ASS. You do have to remove the intercooler, the Y pipe, and I had to disconnect an air hose, as well as a coolant line, just to get to it..... and my knuckles are still busted all to hell.
Oh yea.... also, the gauge DOES NOT COME with the appropriate size fitting... you'll need to go to Home Depot and pick up a 3/8 adapter to adapt the autometer brass fittings to the Subaru hole...... and use LOTS of teflon tape. the LAST thing you want is to redo this because you have an oil leak.
There's a rubber grommet about 1.25 inches in diameter just above the clutch pedal. I drilled holes in it to route the capillary tubing through. That worked for the oil pressure gauge as well.
Split the line just above the factory bov, slip in the "T" fitting, and hook up your capillary line..... plain and simple. I recommend using some hose clamps to make it tighter, as the Autometer T fitting seemed a bit loose in the factory lines.
Yes... it works (at least on an 06 it does).... nothing else was needed except what came in the gauge. Theres 4 wires: white, black, red, and purple. White and black are your illumination gauges, and go to the orange and black factory stereo harness wires, respectively. The red wire off the gauge goes to the red wire on the stereo harness. The purple wire????? Easy...
Route the purple wire through the firewall, wrap it in wire wrap, and zip tie it to the frame securely until you get back to the 02 sensor, right behind the first transmission crossmember. There's 4 wires on the 02 sensor...... 2 black ones, a white one, and a blue one.
CONNECT THE PURPLE WIRE FROM THE GAUGE TO THE BLUE WIRE ON THE O2 SENSOR.... piece of cake..... done.
I also re-routed the factory clock/passenger airbag indicator to the din below the stereo. I had to drill a hole in the back of the din, and I also had to "extend" the factory harness about 4 inches. There's 5 wires in the factory clock harness, so be prepared to splice in 5 wires. I also had to cut the side clips off the clock, as it would not fit in the din until I did.
I hope this helps someone... I know I searched for HOURS trying to find this information earlier today, to no avail (excluding the oil pressure gauge thread).
If there's any questions, go ahead and ask... I just finished the job 30 minutes ago... its still fresh in my mind. In fact, I havent even put my tools away yet.
Good luck everyone.