This is it, the comprehensive tutorial for all 04 model WRX & STi HVAC w/ Keyring Modification guide. So, I know this is a year late, but it's pretty hard and scary to do if you've never done this before. Unfortunately for the 05, you can only do the keyring mod. I haven't found a way to the HVAC. You can also use this guide to do the keyring light mod on the MY03... sorry MY02 fellas, you have no keyring light. As for you MY02 and MY03 guys, you'll have to get 2 #24 bulbs (unfortunately, this has not been tested yet since those bulbs just came out and I don't have ready access to an MY02-MY03 to for testing). Lastly, it's even harder when you do it for someone else! Haha, well, this is the second STi I've done aside from my own, so without further ado:

1) Knowing what tools you need
2) Which bulbs are needed and where to purchase them
3) Bulb differences
4) Modifying The Cup & Wiring the LED
5) Take a step back and check out your handy work!

All right, now that we have the chapters/sections assembled, let's move on.

Section 1 - Know your tools

For the tools, you'll need a few things:
1) Drill type tool to drill a larger hold in the LED holder (I used a Lithium Ion cordless Dremel)
2) Saw type tool to cut the LED holder to a shorter length (Same as above, used the Dremel)
3) Wire clippers
4) Needle Nose Pliers
5) 2 Hours of your time (unless you're just Mr. or Mrs. Model Assembling Hands)
6) Maybe a beverage, beer is not recommended as this job is pretty tedious.
7) Materials - extra wiring (thin type, thin as your hair, you can get this from any old wiring you may have laying around), #74 Focused LED Bulbs (Color of your choice, red or white is recommended, you'll need 4), #74 Incandescent bulb (You'll only need one, it's for the keyring light).
8) Lastly, you will need a lot of patience. This is not a project for someone who wants to bang through it - you will probably mess up your first time, and if you don't, well, go be a surgeon or something!

Dremel tools below:

Section 2a - Bulbs

If I was to do this project again, I would go ahead and order extra OEM bulbs from subaru parts. The part number should be: 72350FE010. To order the LED bulbs, you will need to go here:
You will need 4 Focused LED bulbs with the plastic bottom for your HVAC, and 1 Incandescent glass bulb for your Keyring light.

Section 2b - Bulb Differnences

The OEM bulb is a shortened glass bulb with extra long wires in an extended LED cup. Why did they do this? I have no clue. The LED you're going to use is going to be longer than the OEM bulb when you take it out of the cup, hence the need for all the tools. It's not instant plug and play, it will require some modification. Check out the picture below to see the difference in the bulbs, before any modification.

After you take out the OEM bulb from it's holder, it will look like this.

I originally thought I could just take off the plastic housing on the new LED and shove it into the OEM holder, but I was wrong. As you can see below, the LED has two resistors soldered in - yes, it's an actual LED.

Section 3 - Modifying The Cup

This is the hardest part of the whole process. I'm warning you now, it takes a while to get the LED to sit right. You may have to test the LED cup a couple of times, it is a trial and error process.

When you've mustered the courage, this is what you must do.

Remove the OEM bulb with the green condom on it from the bottom, you must undo the wires. Once you untwist the wires at the bottom, you can slide the bulb out with ease. Save the black LED cup! The OEM bulb can be thrown away. Take your drill type tool and take a set of needle nose pliers. Use the pliers to hold the cup in place at the base. I held it right above the larger circular shroud so I could get a good grip on it. You want to drill into the holder and all the way down. Make sure you hit the very bottom, but don't take out the whole bottom, it will let your LED sit better. Be sure you drill to the bottom first to make the rest of the process easier!

After you've done that, grab your pliers again and take the cutting tool. Chop off about 3-4 mm's of the housing. Don't go too far, you'll have to make your own judgement about how far you want to chop the housing. This way the LED will sit flush.

In order to get the LED to fit, you have to put the drill tool back to use. You have to widen the inside base of the cylinder for the LED to sit correctly. Take the LED and bend the wires straight down. Try fitting the LED, if it doesn't fit, widen the cup some more.

It should look like this and sit like this when you have widened it enough.

Notice how the modified new bulb sits. It's almost the same length, but it fits perfect in the cup. Make sure it seats! After seating the new LED, you will want to bend the wires into the sections that are hollow. Notice on the bottom of the cup how it has hollow spaces. Bend it into that space and bend it over.

Take the thin wiring you have and wrap it around the wire and the cup (you'll see the spaces for this, notice in the next picture how it's wrapped, that is the contact point for your HVAC area).

Notice in the next picture how it is wrapped on the bottom and on the top. I apologize for the blurriness, but these things are small and I was getting pretty tired. The LED should seat without any issues of sliding out of the cup. If you're worried, put on a thin layer of black electrical tape around the LED and the cup. I personally did not do that, as the holes for the LED cups are a tight fit in the HVAC unit.

Now, once you have that done with the first one, the rest should be exactly the same. Take your new LED's and plug them into your HVAC. Have the key out of the ignition when you plug them in and your lights in the off position. If you see a spark and your HVAC doesn't light up (cause you decided to not pull your key out and turn off your lights), don't worry, you just need a 10 ohm mini blade fuse. Once the LED is back into the HVAC, try turning it on and testing the bulb. If it doesn't light up, take that bulb out, turn it 180 degrees, and try it again, it should light up. Repeat and rinse 3 more times.

Section 4 - HURRAY!

Well, now that you've tested it, put everything back together. Take a step back and turn everything on to admire your handy work. Guess what? You're DONE AND IT LOOKS GREAT!!! CONGRATS!

Here are some pictures of what my interior looks like in white vs my friends interior in red. You can decide for yourself which one you like more . Good luck modifying. If you need help or want me to do it for you, PM me and I will see what I can do.

Hope this was helpful to you. If you liked my DIY, have questions or comments, whatever, go ahead and post them up! Found a better way to do this? POST IT

Good luck to you all in your ICE mod.