August 10, 2011

Rear Window Defroster

I'm not quite sure how this happens, but when I bought my car, some pieces of the rear defroster grid were missing. As a result, only about half of the rear window would defrost, limiting rear visibility. In Virginia, it's legal to have your rear-center view obstructed, so long as you can see out of both side mirrors, but I prefer to be able to see as much as possible.

I set out to find a suitable kit. You can pay a lot of money for these things if you want to, but Advance Auto Parts had a reasonably-priced kit for $12.49 online. I think it was actually a dollar or so more in the store. A similar deal is available on Amazon. All I really ended up needing was the conductive paint and the applicator.

Permatex Complete Rear Window Defogger Repair Kit

The kit comes with everything you need to get your defogger working if you have a broken grid or detached tabs. My tabs were fine, so I only needed part of the kit.

Instructions are pretty simple and straightforward. Clean the glass with the included alcohol pad, stick the template to the glass in the appropriate place, and brush on the conductive paint.

I started using the kit by the instructions included, and it ended up looking horrible. The included template is too wide and not long enough, so it makes a wider-than-necessary mark on the glass and has to be moved multiple times. After realizing this, I decided to make my own.

 The tools I used: a strip of masking tape, a smooth cutting board, and a sharp knife. Not pictured: a good straight-edge (steel ruler). It might be better to use a box cutter with a fresh blade than a pocket knife, but this worked fine for me.
 I just eyeballed the width. I had the template from the kit (upper left) for a scale reference. It worked out well. Masking tape is cheap enough that you can make multiple attempts if you need to. If it hadn't worked out right the first time, I would have measured and done it the precise way.
 My custom template on the glass. It took a few attempts to get it aligned properly. Sedans make for an awkward angle for this project. Just be patient and you'll get it.
 This picture shows one of the lines I made with my custom masking tape template. You can see how it bled under a little bit. I scraped the excess off with a knife.
 The entire project area. You can see in the top half how wide the original template is compared to the grid lines.

Overall, the results were good. I haven't had an opportunity to use it yet, so I can't be sure if it works. Testing with an ohmmeter doesn't help. There are practically 0 ohms between lines on the grid, so there's no real chance of finding a break on one line. The best I could do was to stick a probe at a few points on each repair to ensure that current would at least flow from those points to one side or the other. That testing failed to find any problems, so I'll assume the fix was successful until proven otherwise and report back when I know for sure. There's still some cleaning up to do after using the standard template, but at least it should afford me some rearward visibility.


  1. One possibility to confirm there is connection or not would be if the generated magnetic field is strong enough to be detected.

    I assume the heater is fed with 12 V. Now, let's guess that each horizontal line develops 1 W of power. Seen from a distance of 5 mm, this generates a magnetic field of 3 µT. For reference, the magnetic field of Earth is something like 10 times stronger.

    If you could measure that, you would see if your repair worked. It might not be worth the hassle, though.

    1. That's a good idea. I'm sure it can be detected with expensive equipment, but I'll have to see if I can pick it up the cheap way with a compass. Thanks for the tip.