you gotta look for the wire the dims the gauges.. never really tried it on a wrx but when i hooked up a tach onto my friend civic, i jus took the dimming **** out and tested it on each wires.. if the lights on the gauge can dim, it's possible... i guess jus find wiring diagram for the car

 

OK....pull the radio out, carefully, and there is an unused plug on the radio harness...peel the tape off it and use the plug for gauge light(only light!!!) power. I have Autometer gauges and I use a 168 bulb in them, colored with a green marker and they match as close as possible to the '02 gauges.

There ya go, Zipps

 

The dimming circuit in a subaru is a little different than other cars - most use a floating high (0 to +12V) and a fixed low (ground - 0V). Subaru, on the other hand, thought it would be cool to use a fixed high (+12V) and a floating low (0 to -12V) - if you have a mechanical gauge, you can get the gauges to dim by using those two wires as the high and low - for an electronic gauge, it gets a little more complicated, and extra circuitry is required (see below)

 

If your gagues seperate the light from the rest of the gauge power...you are there. Just use the plug on the radio harness...polarity won't matter for the lights, just get some spade connectors from Radio Shack and crimp them on wires to go the the plug...now power for an electrical gauge like an EGT needs to be tapped form elsewhere...I used one of the unused relay plugs in the fusebox for ign. switched power.
The bulb in the gauge may be changed to regulate the amount of light they give...that's why I put #168's in my Autometer gauges...they simulate the amount of light the cluster gauges give almost exactly and dim at a constant rate with the cluster gauges.

 

Oh - come on now, it's not that bad - everything you need can be had at Radio Shack - you just need the op-amp, the diode, the resistors, some wire, and a soldering iron - a box to put it in is nice, too.

I run my gauges at full-bright, anyway, so I just wired my Omori electronic gauge up using the illum lead on the clock (which is 0 when the lights are off, and +12V when they are on) - I have the stuff to set up dimming, but haven't bothered yet (you need to grab the other illum wire from the radio or somewhere like that)

 

The lights, ONLY the lights, for the gauges to the plug on the radio harness...two wires....two contacts on the plug--- dosen't matter which is which for the lights....power for the gauges to function....get that elsewhere....the plug on the radio harness is for dimming the lights...the gauge uses 2 seperate circuits---one for light and one for the function of the gauge....
You must think of it as 2 seperate electrical entities.

 

Most electronic gauges use a common ground for both the illumination (lights) and operation of the gauge - even in gauges, such as Omori, which has two ground leads, they are the same wire (if you measure the resistance between the two grounds, it is in the milliohm range - I was hoping they were discrete circuits, but they are not) - since the Subaru system uses a floating low, you can't use that as ground for an electronic gauge - if you do, then as you dim the gauge, you will be reducing the driving voltage for both the light circuit as well as the rest of the gauge, causing it to shut off (probably when you get much below 10V the gauge will shut down)

With a mechanical gauge, the only circuit is the light circuit, so you can get away with using the high and low illumination leads, thereby preserving the normal dimming function.

 

I guess, by accident, that some Autometer gauges do indeed have an advantage over some of the other brands....and it isn't quality...

I was unaware of the facts of above post and apologize for any confusion that I may have caused.
Thanks, DrD for setting me straight.