Tech Article Title Author Date
Auto-Dimming Mirror Upgrade Steve Brown 2001

Disclaimer: I, in no way, am responsible for anything you do to your car. I have plenty of recorded evidence of, and witnesses who will testify to, the fact that I am totally insane and, therefore, incapable of having advised anyone of anything.

So you want an autodimming mirror like the new Audi's have (I sure did...even my 1995 Ford Bronco had one). I didn't want to pay dealer prices, so here's what I did:

Tools/parts required:

1. Auto dimming mirror
2. Metal mounting button (might be required, keep reading)
3. Mounting adhesive (might come with a new mirror)
4. Some mirrors have a set screw...mine used a T-10 torx screw, so you may need a torx bit.
5. Glass cleaner
6. Razor blade
7. Soldering iron or butt connectors (if you buy new, you may get all the wiring/connectors)
8. Some small gauge wire (18ga is good)
9. Heat shrink tubing (optional)
10. Electrical tape
11. Multimeter

Steps required:
Step 1:
Locate and acquire an auto dimming mirror. You can get one on eBay for cheap (mine was $25) or go to and buy one for $99 (or one with a compass and temp sensor for $249). If you buy a used one, you may have to buy the mounting "button" at an auto parts store (I did...they should let you take them out of the package to test, so take the mirror with you...mine was another $3).

If you bought a used mirror or one without wiring diagrams, determine wiring! On mine, there were three unlabeled wires (and a covered port for two more wires...I think it's for either
turning on the headlights after dark or for side mirrors...I left them alone). I used a 12V DC
converter from an old answering machine to test the wires, you can do that or rig up test wires from your car (12V and ground). Test the wires to find which requires power and which  requires ground. Do this in a well lit area. Cover the REAR facing light sensor with a piece of tape and hold your hand over the front one for a second, then remove your hand (this simulates nighttime with headlights to the rear). When you get the wiring right, the unit will darken...and believe me it's not a "I think it worked" thing, YOU WILL KNOW IF YOU GOT IT RIGHT!

Ok, on mine, a (possibly 1991) Gentex unit, the wiring (when looking at the harness from above with the mirror facing you) from left to right is: Reverse circuit, ground, positive 12V.

Step 2:
Remove your old mirror. My 99.5 required gentle tugging (I parked in the hot summer sun to
get it good and warm). Careful, you could pull some of your windshield off if you aren't careful. I suggest some gentle twisting-rotating motions in both directions to really put the load on the glue first. DON'T just pull hard...the windshield is a $250 replacement at most places... CAREFUL!

Step 3:
Test fit. This is a replacement windshield and had a big blue dot on it for mounting the mirror. Turns out it was a bad location even for the stock mirror, because I couldn't flip down the center sun blocker; the mirror was too high. So test mount (just hold the new mirror up) and find where the metal button needs to be located. On mine, the top of the metal button needed to be just barely above halfway up the blue dot. The nice thing about the blue dot was that it was perfectly centered, so I only had to worry about vertical placement...horizontal was already taken care of.

Step 4:
Clean the windshield...I used a razor blade first and then some glass cleaner.

Step 5:
Use the adhesive kit to mount the new mirror. Mine required (and included) using a primer spread the primer on the mounting button and let it dry for 2 minutes. Then a dab or two of adhesive goes on. Then hold the mounting button to the windshield for 30 seconds
(DON'T MOVE...I used the 1000-1, 1000-2, method so I wouldn't move at all to look at my watch and went to 45 just to be safe). Wait ten minutes before mounting the mirror to the button.

Step 6:
Wiring: my used mirror came with a three wire hookup: Positive 12V, Ground, and Reverse light circuit. I used the positive and ground from my radar detector, since it was already wired and close by. Use electrical tape and/or heat shrink tubing to cover all your work.

(6a) If you want an independent circuit, my recommendation is: Use a multimeter to find an open fuse that turns on when the ignition is on. Put a spade connector on a wire, plug into the empty fuse socket with an inline fuse (5A is good). Put a ring connector on a wire, attach to that nice bolt in the center of your fuse box. Run these two wires up the outside of the A-pillar, cross over at the top...then run along the headliner to the mirror.

(6b) If you bought a new mirror with all the wiring ready to go, just plug in as in step 6a and route the same

(6c) If you, like me want to power off of your existing radar detector wiring, just tap in to the radar's wiring. I went the extra step of opening the wire casing and soldering in the
new wires, but you can use tap-splice connectors also.

(6d) the reverse circuit requires 12V when you're in you need to tap into your reverse light circuit. I haven't hunted down that line in my car yet, so I can't help here, but you want to run a line from that circuit to the Reverse wire in the mirror. This "undims" the mirror when you're in reverse to help you see to back up.

Step 7:
Enjoy your new auto dimming mirror! Mine has a min/max/off setting, some have OFF/AUTO, so if you have multiple settings SET THEM WHEN YOU'RE NOT DRIVING, then take a test drive! Best way to have an accident is by paying attention to your new toy instead of the road!

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