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Everything you ever wanted to know about auto dimming rear view mirrors


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Seeing as to how I'm frequently asked about information on self-dimming mirrors, I thought it would be a good idea to start an informative thread outlining how the mirrors work, the different brands and kinds there are, the pros and cons to those different kinds, as well as basic removal and installation instructions. My goal is to make this as thorough as I can, but if you still have some questions I didn't go over, please feel free to ask. I'm not an expert by any means, but I've been fascinated by these mirrors ever since I discovered them 10+ years ago, so I have gathered a decent amount of information about them. Forgive the quality of the pictures. I will update this post when I get a better camera and more ideal lighting.



Quick History & Background


Auto-dimming mirrors are nothing new by any means. The electrochromic technology used to make today's mirrors has been around since the '40s, and has been in use in automotive mirrors since the '80s. The concept of an auto-dimming mirror was first introduced by the Zeeland, Michigan based electro-optical products manufacturer Gentex Corporation. They created the world's first electromechanical mirror in 1982, which found its way into higher end American luxury cars as an option in 1983. It used sensors to detect glare from behind. The sensors were connected to a small motor that would move the angle of the mirror to adjust accordingly. In other words, it basically acted as an automatic version of the flip tab on standard mirrors. These mirrors would be available through '91.


In the meantime, a father and son team of chemists convinced Gentex that they knew how to apply electrochromic technology (a gel that darkens when electrically charged/clears with no charge) to their mirrors. After investing a lot of money for R&D, they found a way to sandwich a thin layer of the gel between 2 pieces of glass, and have it react to an electrical charge initiated by sensors mounted on the front and rear of the mirror when they detected glare. The first electrochromic self-dimming mirror was introduced in '87, and was made available in the '88 Lincoln Continental, and 8 GM cars in '89. They became more commonplace in the early '90s.


It is at this point that Holland, Michigan based Donnelly Corporation, another major automotive mirror manufacturer, came into play. Gentex' auto-dimming mirrors were a huge success, gaining more and more car manufacturer contracts. Donnelly was trying desperately to take back some of the market share by producing mirrors with very similar technology. In may of '90, Gentex sued Donnelly over patent violations. Through a mess of suits and counter suits over the next few years, as well as out of court settlements, things finally cooled down between the companies. In the meantime, Gentex continued to expand upon what they started with their mirrors. In '93, they introduced the first self-dimming mirrors with a compass that showed the direction you were headed in a little digital display within the mirror itself. These mirrors would become available on '94 model year luxury cars. From '97 - '98, cars would start receiving self dimming outside mirrors, inside mirrors that displayed compass as well as outside temperature, and compass mirrors with LED map lights, which were ONLY available as an option on the Intrigue GLS in '98. The GLS also had this same mirror available in an OnStar equipped version.


Fast forwarding to today, Gentex has grown immensely, and is regarded as the leading company in auto-dimming mirrors with distribution in several countries, including Germany and Japan. They have expanded their contracts to almost all car manufacturers around the world, and self-dimming mirrors are no longer something reserved for higher end luxury cars. They can be found in all sorts of makes and models in many variations. The features have also increased dramatically, including versions with HomeLink, back-up camera and navigation. Meanwhile, Donnelly lost a lot of ground in the war for market share since 2000, and is virtually non-existent in the manufacturer's contract department.



Gentex vs. Donnelly Pros & Cons


Being the 2 major producers of auto-dimming mirrors, these two have been dueling each other for a couple decades now. Virtually every feature Gentex came out with, Donnelly would copy. However, the 2 companies took a very different approach as far as aesthetics. Donnellys had more of an "egg shape" to them, especially if they had temp and compass, because they put the display for those in the base of the mirror as opposed to in the mirrors themselves like Gentex does. The front of a Gentex mirror looks more like traditional mirrors, but with a bit of an extension at the middle of the bottom for the buttons. Personally, I prefer the way Gentex' look a lot more, but that's subjective. One plus for Donnelly mirrors is that they are much more commonly available with map lights. Since most of the vehicles that Gentex' originated in were luxury, or well equipped, they usually already had some kind of fancy overhead console or dome light, so they scarcely received map lights in the mirrors.




Fully optioned Donnelly mirror.


However, this and all other advantages for Donnelly mirrors are a moot point because of one monumental problem they're prone to which renders them useless. Donnellys are notorious for breaking and leaking the liquid inside of them, often causing discoloration in the paint when the liquid eventually drips onto the center console. Why is not completely known. However, I mentioned the legal troubles between the 2 companies earlier, and that Donnelly had to change their methods of accomplishing the auto-dimming effect due to patent infringements. My theory is that whatever they did to change the process for auto-dimming, it was an inferior process with poor reliability/durability. On the other hand, I've never really heard of a Gentex mirror failing in any capacity (certainly not by leaking out the gel). It is for this reason that I usually suggest people switch to a Gentex when their Donnelly mirrors finally fail, which they inevitably will.


Mmkay, now for the good stuff you've been waiting for.



Removing and installing auto-dimming mirrors


Removing factory auto-dimming mirrors from the windshield


*DISCLAIMER: The process for removing mirrors with the newer mounting style can put your windshield at risk for cracking or breaking. I am not responsible for any damage. Attempt at your own risk!


This will actually be the hardest part of adding/replacing an auto-dimming mirror. Rather than using the traditional, easy-to-remove single torx screw to tighten the mirror onto the windshield button, newer auto-dimming mirrors have a tensioned spring with tabs in the brackets that, once the tabs clear the windshield button, locks it into place, making removal a serious pain by comparison. To get an idea of what you’re dealing with, here is a mirror off the car with the spring/tabs exposed (tabs circled in blue). It is this spring that has to be pushed in towards the mirror so that the tabs on the spring will clear the mounting button, allowing the bracket to slide up and over it.





You will basically have to insert a small slotted screwdriver into the slot opening at the bottom of the mirror bracket’s base, and gently tap at the screwdriver (preferably with a rubber mallet) till it pushes the tab back far enough to clear the button. The screwdriver is in far enough when it won’t fall back out with little force, but at the same time, not so snug that it takes a lot of force to get it unstuck. Take your time, and check to see if it’s at this point with every few taps. Driving the screwdriver in too far can cause the windshield to crack or break. Here’s an off the car visual to give you an idea of what you’re looking for.





At this point, the mirror bracket should slide out by gently lifting UP on the mirror while wiggling it back and forth.




Again, I have to stress to be extremely careful with the removal of these mirrors. The process itself sounds straightforward and easy enough, but the springs are often stubborn, so you have to be very cautious not to exert enough force to break the windshield.


Tip: If you do not feel comfortable trying to remove the mirror yourself, skip to the wiring so that’s in place, and then take the vehicle to a glass or body shop to pop the mirror off. Most will remove rear view mirrors for $10 - $15, and many will even do it for free! Same with reattaching mirrors that have fallen off!

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Replacing/swapping factory auto-dimming mirrors


If your vehicle already came with a Donnelly or Gentex, and you're looking to swap mirrors for more features, or because your Donnelly broke, then this will be a fairly easy process, as all the essential wiring will already be there. The first thing you will need to determine is if you have the older style 3-pin harness, or the newer style 7-pin harness, as illustrated below.




If you have the newer 7-pin style with only 3 wires coming out of it, then this will be a direct plug and play. If it is a 7-pin, but there are more than 3 wires present (i.e. your current mirror has map lights), then you will simply pull out the extra wires from the harness, and either cut them off at a point where you can’t see them anymore, or if you’d prefer to keep them in tact, wrap up the tips to prevent any electrical problems, and tuck them away in the headliner. You can then just plug in your existing harness into the new mirror.


If you have the older 3-pin harness, this will still be an easy swap, just slightly more time consuming/involved. Without loosing the order the wires are aligned in, remove the pins from the old harness with a small flat screwdriver. Do the same for the wires coming out of the harness on the new/replacement mirror.


Mirrors7.jpg Mirrors8.jpg



Next, with the new harness facing in the direction it will be in when plugged into the mirror, and the wires from your vehicle aligned in the same order they were in when removed from the old harness, push the wires from your vehicle into the pinouts in the new harness from right to left. A pin-out is provided after the next section.


Mirrors10.jpg Mirrors11.jpg


Mirrors12.jpg Mirrors14.jpg




Installing auto-dimming mirrors in non-factory equipped vehicles


If your vehicle came from the factory with a standard mirror, don't worry. An auto-dimming mirror can be installed into ANY vehicle with a very small amount of electrical know-how. All it will require is one wire running to a +12v that powers on with the accessories, and one grounded wire. The self dimming and compass features are self contained and need only that one power wire to function. The 3rd wire automatically disables the self-dimming feature when the vehicle is put into reverse, but most people seldom wire it, as it is an unimportant feature and not worth the trouble. If you have a mirror that shows outside temp, you will need to get a temp sensor as well, and run a wire from the sensor to the mirror. Whether you have a 3-pin, or 7-pin harness, the following is the correct wiring for the majority of auto-dimming mirrors with or without compass when looking at the front of the mirror with the harness plugged in. Obviously ignore the 7th pin if your replacement mirror doesn’t have map lights.






And that’s all there is to it! If you have any questions I haven’t gone over, please feel free to ask. BTW, I have amassed a rather large collection of fancy mirrors of all types, and will be posting a thread for them in the classifieds section soon. I will provide a link here when I do. All my mirrors are tested prior to sale as well. As a general idea, an auto-dimming Gentex or Donnelly is $55 shipped within the continental US. A Gentex with a compass or Donnelly with map lights is $70 shipped.

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However, the 2 companies took a very different approach as far as aesthetics. Donnellys had more of an "egg shape" to them, especially if they had temp and compass, because they put the display for those in the base of the mirror as opposed to in the mirrors themselves like Gentex does.


Earlier Donnelly mirrors had the compass in the mirror glass like Gentex. The body is identical to the non-compass mirror. The VFD is green instead of aqua like the Gentex.

I remember buying mine from some GP store during the transition period and I specifically requested the one with compass in the glass because I liked it better.

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Actually, I don't know if those were earlier ones. I think they were available around the same time as the egg-shaped ones. However, very few cars got those (some Chryslers/Lincolns I can think of off the top of my head), so for the sake of keeping this simple, I didn't want to go over that bit. I actually have one of those mirrors, which I had always wanted because they were available with map lights. However, despite the fact that it's been sitting in my collection bin of mirrors in my obviously climate controlled apartment.....it broke anyway. :gr_mad:


Eventually, I'd like to expand upon this post with pics of as many different models as I can get. Maybe even a video at some point.

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I believe they're earlier because I remember wanting one in the late 90s and the style with the compass in the glass was all they offered at the time in aftermarket channels. At almost $200, I put off buying it for a couple of years, and then I saw every place selling them was switching to the newer version with the compass/temp below the glass, this was around year 2000. Thinking if I waited, the old version would disappear forever, I panicked and finally decided to drop the cash. I remember emailing the ClubGP Store (where I think I bought it) and asking if they still had any of the old style still in stock, and they did so I bought one leaving a note to be sure and send me the old version.


Yeah, my cars are garaged and the TGP never leaves the garage, but the Donnelly mirrors still leaked out anyway. Gentex have been pretty awesome though. I also like that you can open the early 2000s Gentex with a credit card, they're snapped together, not ultrasonically welded together like Donnelly. That makes it possible to repair a really rare Gentex like the one with map lights using parts from a non lighted mirror.

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I don't think they were replacements. Both designs were offered simultaneously to different car manufacturers. For example, the one that you had with the compass in the glass was offered in late '90s/early '00s Jaguars:


2003 Compass in glass mirror

2003 Egg-shaped comp/temp mirror


I think the reason there were more of the egg shaped ones for sale is because they were more common. I'm not sure when they stopped making either mirror, but I cannot recall seeing a car come with either since around the mid '00s. I know the self-dim with/without map lights (depending on overhead dome option) were used in the Gen II w-bodies that didn't get OnStar mirrors (which were made by Gentex). In fact, the constant questions from failed mirror w-body owners is what prompted me to put this piece together. Got sick of going through the same info over and over again, so I decided to put just about everything I've ever been asked in one post.


And yeah, what amazes me is that you can take a Gentex mirror apart, but they dont have problems, yet a Donnelly mirror that can't be opened still manages to leak.

Edited by RareGMFan
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Things may have been different for OEMs, but in the retail channel, the compass in the mirror was older. Every online store that sold Donnelly compass mirrors as an aftermarket add-on (JC Whitney, Club GP Store, etc) had the version with the compass in the mirror throughout the late 90s and into early 00s, but around the same time, they all changed to the one with compass below the mirror and you couldn't buy the other one. I imagine OEMs were different because they could order whatever design they preferred.

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Oh, I don't know about the brand new retail sales. Never looked into those on account of how expensive they were new. I'd only visit Gentex' site periodically to see what crazy feature they had added on now to their mirrors. Anyhow, it's a moot point since all the Donnellys break eventually anyway. Still upset my in-mirror compass one broke.

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Yep, the Donnelly ones are crap. I did see there is a repair service, but it's $95+S&H with no guarantee they can fix it. If THEY damage your housing beyond repair trying to get it open, they'll give you an $80 refund and you get to pay S&H to get your ruined mirror sent back to you, if you want it.

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