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

[RareGMFan]

Sorry I didn't see this post earlier. How do you know the auto-dimming isn't working? What method have you used to test it?

 

[loopy smurf]

Sorry I didn't see this post earlier. How do you know the auto-dimming isn't working? What method have you used to test it?

If headlights behind you are blinding you through the rear view, the auto-dimming probably isn't working...

Sorry - couldn't help it...

 

[EJOUIE]

Are the mounts different from the two brands? Do I need to re-glue a button if I switch?

 

[RareGMFan]

If headlights behind you are blinding you through the rear view, the auto-dimming probably isn't working...

I ask because I've had people think it's something really obvious that you can clearly see. You usually can't. It does its job when it's dark out, and you're getting hit by bright lights from behind, so you don't even see it getting dark. The best way to clearly test them is to cover the sensor on the front during bright day light. The mirror should get dark pretty quickly.

Are the mounts different from the two brands? Do I need to re-glue a button if I switch?

99% of the cars with the windshield wedge mounts are the same size. I've used mirrors from GMs, Chryslers, Fords, etc with one another. Once every great while, there will be some kind of weird variant, but it is pretty rare.

 

[LS1GTP]

So in my 2000 GP, I have an autodimming mirror with map lights. If I swap to another autodimming mirror with the compass and map lights, all I need to do is plug my pins into the larger connector and it should work?

 

[RareGMFan]

Yes. However, Gentex mirrors (the better brand) with compass AND map lights are pretty hard to come by. Only the Intrigue GLS, and a small handful of Lincolns (possibly the Chrysler Sebrings, too) got them because the cars they came in usually had map lights in the overhead dome/console. It's the only downfall to Gentex.

 

[LS1GTP]

What about using this one instead?

GM Grand Prix OnStar Rear View Mirror '98 03 Compass | eBay

 

[RareGMFan]

That's an OnStar one that was standard on the '01 & up GTPs. They don't go for much because either your car already came with one, or you don't want one. They're big and bulky, and the OnStar is useless since it's analog, and GM moved to a digital signal years back. They also have a 2-row 16 pin harness vs. the 7-pin of the non-OnStar mirrors, and you're still loosing the map lights, too. You can certainly use it and wire it to work (minus the OnStar part) just like any of the other mirrors. I'm just giving you the cons. BTW, you'll need a separate temp sensor attached somewhere by your front bumper and then wired to your mirror in order for the temp to display properly.

 

[99GTPMLA]

Sorry I didn't see this post earlier. How do you know the auto-dimming isn't working? What method have you used to test it?

I figured it out. Apparenetly the auto dimming mirror runs through the sunroof fuse. Since I don't have a sunroof, I didn't think to check it. I read about it online and found the fuse was bad. After I replaced it, it started working fine. Since that, I bougth a Gentex-177 auto dimming mirror with compass and switched it out. Now I can tell which direction I'm going.

 

[epon]

Great info! Is there a How-To for converting the 3 pin wire of a 2000 GTP to the 16 pin harness of an On-Star mirror? Cant seem to find one. Thanks !

 

[Slappyn]

Yea I am looking for the same thing. I bet that once power goes into the mirror the compass and what not will light up. I bet that all those other pins were for all the on star crap. So try to rind power for the overhead lights, for the mirror and the signal wire to disable the auto dimm in reverse and you should be good. I however, cannot even get the plastic cover off without breaking it but I have a strong rear window tint so Im ok with it for now. Once I get some of these pokers out of the fire, rebuilding second vehicle and fixing GTP I will post back here. Let me know if you figure it out please.

 

[RareGMFan]

You are correct, Slappyn. Just like any electronic mirror, there is only one +12V wire to power the auto-dimming, compass and temp, though in order for the temp to display properly, you will need to get a temp sensor (installed near the front bumper) and run 2 lines (pos and neg) to the mirror from it. The rest of the pinouts on an OnStar mirror are for things you either don't need, or can't use. According to the diagram below, with your current harness facing you right side up (the tab should be at the top of the harness), the first wire furthest on the right will go to pin 13 of the OnStar harness ("on with ignition" power source), 2 will go to pin 8 (negative), and 3 will go to pin 9 (your "disable auto-dim in reverse" feature).

 

[RareGMFan]

Thought I'd update this thread with some new findings. My disdain for Donnelly mirrors has grown. A couple weeks ago, I literally had 3 of them not functioning properly when I tested them. I had noticed on my first failed one that the power for the compass, map lights and auto-dim would flicker when the wires moved. I wasn't sure what was causing it at first. I thought maybe the wires to my power supply were not getting a good connection, or moving, etc. Then I wiggled around the harness that was plugged into the mirror, and noticed it consistently flicker with movement, so something was loose from inside. Terrific! It was not worth the 1.5 hour round trip drive to get credit for it at the yard, and I couldn't sell it not functioning, so I figured I had nothing to lose if I opened it up, which was my first time doing so with a Donnelly (they're not meant to be opened, unlike Gentex mirrors). After wrestling vigorously to get it apart, I found that the 7-pins going out to the harness were loose at the circuit board. So I ran out and bought a small spool of solder and some super glue (to put the mirror back together later). Resoldered all 7 pins, super glued the 2 mirror halves since there's no other way to put them back together again, and plugged her in. PRESTO! Everything worked, despite shaking the hell out of the wires and mirror. Great! One down.....two to go, as I would later find out. :th_angry2: BTW, I sold that first mirror for $120 shipped a couple weeks ago. :th_mischievious: That certainly helped to make up for a lot of the trouble and aggravation.


SO......let's see the current list of reasons why I prefer Gentex over Donnelly...

1. You're not supposed to open a Donnelly mirror. Gentex mirrors can be pried apart with a credit card, or very thin/small flat head screwdriver, then snap back into place. Donnelly mirrirs are glued, or something to that effect, because they have no way to reclose. They will need to be super glued back together if you take them apart.

2. The Donnelly mirrors have poor solder joints. As stated above, I had to take 3 of them apart to re-solder the 7 pins for the harness/wires to get them to function. Granted they were fine afterwards, it is rather silly to have to do this, especially in mirrors not meant to be taken apart. I've never had a problem with a Gentex mirror not functioning.

3. Donnelly mirrors are prone to breaking by leaking the auto-dimming gel. This is the biggest problem with Donnelly mirrors. Almost every car I see in the yard that's supposed to have a Donnelly mirror, it's either gone already because it's working, or still on the car because it's broken (a LOT more broken ones than missing ones). Every time I see a car that's supposed to have a Gentex mirror, it's either gone already, or nobody has gotten to it yet. I've never really seen one broken before, unless some jackass cracked the glass on purpose, or broke it taking it apart for some unknown reason (can't see what you'd be after inside one).




....that will be all for now.

 

[ericspecullaas]

they are looking the hidden $1000 that was locked away in a car many moons ago lol.

 

[buford1972]

My 2000 GTP has the dual climate control which displays the outside temp. Of course my old mirror leaked the gel onto my center console which stained and what lookes like acid burned where the drops landed. I picked up a mirror that has the temp and compass on the display from my local pull-a-part. My question is that since I already have the outside temp probe that my heater display uses, do I need a second probe for the mirror to use? I like the idea of the outside temp display on the mirror much better but would like to also keep the heater temp display functioning. Also, which pins does the signal for the temp probe plug into at the mirror? Can use my existing temp probe to send a signal to bothe the mirror and my heater display? Where are the wires located that would I tap into? My stock wiring is the 3 prong plug and the new mirror (On Star style) is the double row plug.

 

[RareGMFan]

Between this forum and others, several people have tried to tap into the temp sensor wires from inside the car for the climate controls, and found it doesn't work. I'm suspecting this is because for cars with the digital climate control, the ambient temp sensor goes through the BCM maybe? No direct signal from the sensor could explain why the mirror isn't getting a proper signal/info. I don't think anyone has tapped directly into the sensor wires (closer to where the actual sensor is), and run those lines back to the mirror to see if that would work. I can't imagine the sensor itself is any different, so I don't see why that wouldn't work. Easiest way to find out is to test it by tapping directly into the sensor wires (with the mirror outside of the car) before you waste time trying to run them INTO your car only to find it won't work. Though regardless of whether that method works, or you need an entirely different/separate sensor, you are going to need to run 2 extra wires from your mirror to the actual sensor to make the temp display properly on your replacement mirror.

Also, I already went over how to switch a 3-pin Donnelly mirror to a 16-pin mirror. Look just a few posts above at post #32. Should be pin 6 & 7 for the temp sensor.

 

[buford1972]

Perfect! Thank you for the info. Yeah, I saw that previous post after I had already sent mine. I'm thinking that next time I am at the wrecking yard I will just get a second outside temp sensor. I'll hook it up temporarily to the mirror just to see if it works and then go to the trouble of mounting it next to my current ambient sensor and run the two wires through the firewall if it all works. Just to calrify... Pin #6 is the "Ambient Temp Signal" and Pin #7 is the "Low Reference". These are what would make the Temp display work on the mirror? Thanks again for the info and saving a me a ton of time!

 

[RareGMFan]

Yes, and I really don't think it matters which wire goes to which (+/-) as long as both are connected and it can measure resistance. There's no question it will work if you get a separate temp sensor. I just sold this one with the temp sensor, and as you can see in the pics, I hooked it up and made it work even out of the car.

Jeep Wrangler Cherokee YJ TJ LJ JK XJ KJ Auto Dim Compass Temp Rear View Mirror | eBay

What I was suggesting is to see if hooking up the mirror directly to the climate control temp sensor that's already there might work. It may work fine, it may be that having the signal go out to 2 different sources/sets of wires (climate control and mirror) messes up the signal, and it just can't be done. Can't hurt to try it for free, though.

 

[PurpleGuy]

Rare maybe you can help me. Here's the mirror I just got.

And the 7 pin connector.

From what I saw in a previous post the pink should be power and then the black should be negative. Solid green is the reverse wire. And the green stripe and black stripe are for the temp sensor.


When I hook up the pink to positive and black to negative I can't get the screen to come on. The auto dimming function does work but the screen won't turn on. Am I doing something wrong?

 

[PurpleGuy]

Alright after screwing with it for awhile I finally got the display to work. But it's a bit cold in here I'd say

I think a new sensor might fix my issue. The mirror does recognize that the sensor is hooked up. I know this because if I disconnect that sensor it displays "OC" meaning open circuit