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Gentex Rear View Mirror Upgrade

     UPDATED: November 8, 2019                       CONTACT       
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If you have any comments or if you can improve this information, please feel free to email.


After seeing someone install one of these mirrors in their car, I decided it was an upgrade worth pursuing for my Volvo 242.
This mirror came standard on a large number of early to mid-2000s GM vehicles, mainly Suburbans, Tahoes, etc.  The mirror was made by Gentex and there are millions of them.  If you're a frequent salvage yard visitor, finding something like this may not be difficult.  Otherwise, you can easily find a number of them available on eBay. 
This one is the Gentex 177
(sometimes spelled GNTX). 
The Gentex 177 can be easily found like this one above with Compass and Temperature dual display.  Be aware that some have a single display that appears to be Temperature ONLY or some single displays allow you to toggle between compass and temperature by pressing buttons.  If you want both Compass and Temperature to show like the photo above, make sure you choose the correct one that looks like the one above. 

 The mirror I got has a BLUE/GREEN display.
Also there seems to be some mirrors available with a RED/AMBER display, but they seem kind of rare.  I didn't care.
eBay prices seem to vary between $30 and $50 (and higher), so shop around.

I got mine on eBay for under $40 shipped. It included the outside TEMP SENSOR with wire pigtail and the 7-POLE PLUG with wire pigtail.
Be sure to choose one that comes WITH the 7-pole PLUG/PIGTAIL and a TEMP SENSOR/PIGTAIL.

TEMP SENSORS (Two types):
There appears to be a couple different types of sensors. The one I got is the TOP sensor shown above. I don't think there is a difference in how they function.  The sensor should be mounted somewhere outside your car. The usual location seems to be under the front bumper of the car as far from engine or radiator heat as possible.

This mirror mounts on a standard wedge mount. That means there is a metal button that's glued to the windshield. 
So YES, this will be a departure from originality in your 240.
  If this bothers you, then this mod may not be for you.  Stay with your old mirror and suffer!

I briefly considered trying to modify this mirror mount to somehow fit the Volvo 240 roof mirror mounting location, but the effort did not appear to be worth it.  So I mounted this new mirror to the windshield like it's designed to be mounted.

The metal wedge mount windshield button is usually not included when you buy a mirror on eBay, although some sellers do offer one. I got mine separately for a couple dollars.

Differences in 240 Mirrors
<<< If you have a 240 2-door or 4-door sedan, your original 240 mirror will have a plastic cover like these photos.  Your original Volvo mirror can be pulled off with a tug.  If comes off that way as a safety feature to protect your face when you collide into the mirror in a crash.
<<< If you have a 245 WAGON, your original 240 mirror will look like these photos.
I don't have a 245, so I'm going to show my installation in my 242.

<<< As you can see here I have removed my mirror and I have a radar detector. I decided to make a mount for it where the plastic cover used to be. So I'm not using the old plastic cover in my car.

Then I glued the metal wedge mount button onto the windshield.  Make sure you glue it on the correct side and NOT upside down or backwards. PAY ATTENTION!

Before gluing the button, I took some time to check positioning of the mirror by holding it up to the windshield.  That metal button is going to be permanent on the glass, so make sure it's where you want it to be.  I chose to place the top of the button about 2 inches below the top of the windshield.

Failures to Stick!
This seems to happen a lot when amateurs like me do stuff like this.  I used Permatex windshield mirror adhesive (found at my local auto parts store) and followed the instructions perfectly. It says to allow 30 minutes drying time before mounting the mirror. I did and the button then popped off while I was turning the set screw on the mirror mount. 

Attempt #2: I used a wire brush wheel on my bench grinder to clean the hard glue off of the button.
The glue was having no problem sticking to the button, but it was not sticking well to the windshield glass. Then I tried again, this time allowing several hours for drying. I got the mirror mounted and set screw tightened. As soon as I tried adjusting the mirror, the button popped off the windshield again! 

Attempt #3 (see pic): So on my third try I used some 180 grit sandpaper to rough up the glass surface first.

Then I glued again and allowed the glue to dry OVERNIGHT.  That one worked and it has stayed on.

<<< Here's the result.  There's a single set screw in the mounting base that tightens to snug the mount against the metal button. It's a Torx T-20 screw. Make it snug only.  No need to twist hard, especially if your hoping to keep the mirror on the windshield.

Overall this was an easy installation and well worth the effort in my opinion.

Below I'll go over the wiring, programming and a couple other things.  Keep reading.

<<< Here's the outside view of the mount on the windshield.


This connector plugs into the back of the mirror. It has 7 poles (and will probably have 7 wires), but you will only need to use 4 of them. 
Pole #1 is the closest one to the center mount of the mirror.
(Some wire colors are different on some mirrors)
Blk/Wht, Pink or Yellow
+12V switched (key in the first ON position)

not used

not used

not used
Blk/Wht or Green
Temp Sensor (polarity not important)
Blk/Blue or Purple
Temp Sensor

Here are some simple instructions for setting up the mirror after installation.
It covers setting the temperature display (Fahrenheit or Centigrade). It also covers setting the compass zone and compass calibration.

Click Image (PDF document, 280 kb)

DIM DISPLAY Issue and Improvement

<<< The compass and temperature display in this photo doesn't tell the complete story. This photo was taken in my garage.  That display is fairly visible when the car is inside the garage, but when outside on a bright day, it's hard to see. It just seems to be a bit too dim to see well in bright daylight conditions.  This compass/temp display will normally be DIM like this photo in low light conditions. Then it will automatically BRIGHTEN in brighter light conditions to make it easier to see.  But it wasn't good enough in my opinion.

To see how this display changes in brightness, have a look at this short video:

I found that even when the brighter setting took effect, my mirror was still not quite bright enough for me in bright daylight conditions. Below you will see my efforts to get a brighter display.

<<< The light sensor that controls the display brightness can be seen here below the connector plug.  I believe the device near the windshield mount controls the compass function.
Some exploratory surgery was needed. 
I wanted to see if the brightness could be improved. 

This part is totally up to you.
If you break it, don't come crying to me.

<<< Separating the front frame from the mirror body is easy.  Wedge a flat screwdriver in there and slowly twist until you get a POP. Then slowly work around the rim twisting and popping the frame until you've gone all the way around and it comes loose.
The mirror and circuit board will come out together.
<<< Here's the back of the circuit board.  You can see that it's attached to the mirror plastic body by a small harness. 

<<< To free the circuit board from the mirror body, simply unplug that small plug.  It just pulls out.

I know NOTHING techical about this circuit board, so I DID NOT mess with the electronics. If anyone has tried that route, I would like to hear from you.
Here's what I did.  While being CAREFUL with the two small wires still connecting the circuit board to the mirror glass, separate the circuit board from the mirror and turn the circuit board over like this. They aren't glued together.  They pull apart easily.

Here's the front of the circuit board.

That dark blue rectangle is the compass/temperature display. 

<<< That is a piece of dark blue film which is held on with some soft glue on the right and left edges. I inserted a micro screwdriver to gently lift it. Then I could get my fingernail in there and I slowly pulled it off. 

<<< Here you can see the display without the dark blue film over it.  Now I know what you're thinking.

1. You want to know if the display is still blue/green. The answer is YES.  The color hasn't changed, but this does help make it brighter. Keep reading.

2. You're also thinking that display looks really ugly without the blue film.  Not to worry.  Keep reading.
<<< With the mirror glass again placed over the circuit board, this is what you can now see through the window. 

Yes, that image may seem undesireable, but once it's in the car it becomes pretty much invisible. Just wait.

Now you can reassemble your mirror the same way it came apart.
<<< Final installation is complete. Looks pretty good, doesn't it? Compare the OLD photo on the LEFT with the NEW photo on the RIGHT.  The display brightness has been improved.  It's  easier to see now in bright daylight conditions. And that ugly display thing you saw above is not visible.  It's a miracle!

Mission complete. If you install a different mirror in your Volvo, I'd like to hear what you did and how things went.
Email me:


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