Disclaimer: I'll get this out of the way here and now, so it is not missed: There is risk involved in modifying your car in any way. Follow the below tutorial at your own risk. This tutorial is not meant to be neither comprehensive, nor exactly match your vehicle. This is a description of what I did to my vehicle, and I only guarantee the accuracy of this tutorial to match my vehicle. By following this tutorial, you agree to hold me harmless, and understand that there is no warranty either expressed or implied herein, and you may actually void warranties with either your dealer, Subaru of America, or other aftermarket parts that you have. You are going to die some day. The use of the following information may or may not change that date. --There.. Now I feel better.

In one of Trunk Monkey's Color Change Tutorials, someone asked if it was possible to change the polarity of the LCD's color on the odometer. I knew this was possible, but I want to show how to do it. It is really not that difficult a task to accomplish, but the materials that you need are fairly specialized, so it's not something you're likely going to be able to dig around in your spare parts bin to be able to find parts to complete it with.

The first thing you need to acquire is a piece of polarization film. This is used for all sorts of things, namely photography, and can be found from many sources, in various sizes, and thicknesses, for varying costs. I got mine from Edmunds Scientific but it is NOT by far, the cheapest, or easiest way to obtain this material. I got the 2" squares, because I knew that the LCD was roughly 2" across, and I wouldn't have a grip left over that I would never do anything with. Additionally, you need some 'optical laminating adhesive'. Fortunately for me, I work at a company that uses said material on occasion, and I was able to finagle a piece of scrap from someone on the floor. Don't ask, I'm not going to do it for you, but I will tell you what it is, perhaps you can find a way to finagle your own sample. The adhesive I used was MacTac PermaTrans® IP-2100

Here's the principle: LCDs function by the rotation of polarized light by 90°. Meaning, in every LCD screen, there are actually two polarization films, and the LCD element. Both films (one on the front, and one on the back) are aligned the same way to allow light to pass through. If one of them is rotated 90°, then no light passes through. When the LCD displays a 'digit', it again (in between these two filters, mind you) rotates the polarized light 90° which then is the opposite of the background. If you take two pieces of polarization film, and hold them up to a light, you can rotate them until either all of the light is blocked, or all of the light passes through, or anywhere in between. We want to deal with stark contrasts, so we'll keep things at 90° increments.

Principle in action: Before I can change anything, I have to remove the gauge from the car, and dis-assemble it so that I can get to the LCD. In assessing what I needed, I had done this twice before, so the pictures that you see are of my third time through the process. The steps are pretty simple once explained. As in Trunk Monkey's Gauge Cluster Color Change Tutorial, remove the gauge pod from the car. Once you have the unit out, you can begin to take it apart. Mine had the clear plastic cover, a black plastic cowl, a black & silver bezel, the two dial components, the PCB, and a white casing on either side of the PCB. All of this was held together by a number of clips molded into their respective mates, which makes nice for disassembly, just make sure that you disengage all of the clips before you start trying to tear things free.

The dials were held on to the PCB with two metal tangs per dial barrel to hold them on the pins that are on the PCB. Once I figured this one out, I was home free. Be sure that you don't bend these too sharply and stress the metal, because after doing that only a couple of times, they WILL break. After you get these tabs bent out just enough to clear the PCB, then you can remove the dial packages either by poking the metal cans from the PCB side, or by pulling from the white plastic clam-shell side. Either way, do it gently, and evenly so you don't bend those pins.

Now that you have the PCB free, you can get to the LCD display without diversion or interruption. The LCD is lit from behind by a 0.2" bulb that I had previously 'double-bagged' with the 'bulb condoms' found in Trunk Monkey's tutorials, though I got mine from mouser. The original color is green, and that color is created by a colored filter/diffuser on the back side of the LCD. If you very carefully pry the non-pinned side of the LCD up, you can reach in there with tweezers to remove this filter. I had run my LCD for a couple of days without the diffuser, intending to replace it later with a clear diffuser (I say diffuser, because it has a 'velvet' texture on one side, and this spreads the light out a bit) but it didn't seem like I needed it in this application, because I didn't notice any 'hot spots' where the light was focused on the LCD more than any other spot, so I opted to leave it out.

Once the diffuser is out, remove the bulb on the back side, and use a flashlight to shine through it, with your polarization filter held over the front of the LCD. The point of this is to determine the proper orientation of the filter prior to cutting. I first applied my optical lamination adhesive to one side of the filter, leaving the liner on the opposite side of the adhesive. The liner on the adhesive was clear, but on yours it may not be, so plan ahead. My filter had a protective coating on both sides, so I could handle it without getting fingerprints on it. If you have never used optical lamination adhesive before, here's a caution: It is imperative that you have NO air bubbles, and that it be applied in a smooth, uniform manner from one side to the other, or from the middle out (which is slightly more difficult, IMHO) because it is not as forgiving as most adhesives, and it WILL NOT let you work the bubbles out. These bubbles will be visible, and you will NOT be satisfied with your results. In fact, there is a small bubble in mine, but fortunately, the dial overlay covers it, so it's only going to bug me because I know that it's there. So anyway, while you are shining the flashlight through the bulb hole in the back of the PCB behind the LCD (you might want to do this in a semi-dark room), rotate your polarization film until you get the effect that you want. In my case, it was as black a background as possible (remember, without the LCD energized, light will pass right through, and I wanted to invert that) and then mark (on the liner, not the filter) where the edges of your LCD are. When you have it marked (turn the lights back on) you can cut it to size, but be sure to mark it's orientation so you KNOW what result you are going to get. You need to remove the existing polarization film from the front of the display. Do this carefully, as LCDs are essentially two small pieces of glass that are sandwiched together, and they do break. Clean it really well with a little bit of acetone, or rubbing alcohol (I'm not going to get into a debate over which is best; I used both) until you see the shiny glass, not the matte residue from the old adhesive. Do one final wipe with a lint-free cloth to make sure it is clean.

Remember what I said about optical lamination? This is where it becomes really difficult. Remove the liner from your adhesive (already attached to the polarization filter, which is cut to size?) and from here on out, do not handle the adhesive side. Fingerprints are BAD, and you will NOT get them out. There is a bit of a trick to this, because without removing the LCD from the housing, there is no support on the back side, and it is glass, and it will break, but you need to press down firmly, and evenly from one side to the other as you apply your new filter. Make sure that your application is as fluid a movement as you can possibly make, and the adhesive will love you for it. As you apply it, you may get spots that seem to change color, but this is likely a reaction to the heat of you rubbing it, rather than a malfunction, or a reason to panic.

Now you can breathe a sigh of relief.. the hard part is over. Remove the liner on the front of the polarization film, and clean it with rubbing alcohol (acetone might be a bad thing in this situation), and blow off any lint from rags or towels that you used with canned air. Then, cleaning, and blowing of as you go, carefully assemble the gauge cluster in reverse order of dis-assembly. Don't forget to bend your dial-can tangs back over the PCB to hold the cans down. The 'glass' on the front is actually Plexiglass, or plastic, and will scratch VERY easily (and they're a bitch to get out) so don't wipe it with anything dry. Use windex to lightly mist a paper towel to the point of it softening the paper towel (yes, even a dry paper towel can scratch optical plastic) so you can properly clean it. Re-install the gauge in your car, and connect everything back up, and check it out!

One final note: it helps to have someone looking over your shoulder to keep tabs on things in their non-diluted mind to keep you sane, and doing things in order.