How To: Install a Compass / Temperature Rear View Mirror

Discussion in 'OEM and Custom Interiors' started by borahshadow, Oct 29, 2011.

  1. borahshadow

    borahshadow I'm Awesome

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    Dec 4, 2010
    I've wanted to do this mod for a while now. I finally got a chance to go to the yard and pick up my mirror. There is some information on this mod in various places on this forum but I hope to consolidate some of it into one place in an easy to follow guide.

    1. Get yourself a mirror. These mirrors can be found in various models of GMT-400s I don't know specifics about which years and stuff but I know that they are usually found in more recent model GMT-400 SUVs but they can be found in the trucks too. The information here should work or be easily adaptable for other mirrors. Especially other GM mirrors like those from a Cadillac or GMT-800.

    When you get your mirror these are the things that you MUST get also.
    1. The Mirror (duh)
    2. The Temperature Probe (This is usually found in the grill area)
    3. A wiring pigtail for the mirror (at the least just clip off about 6" of it)
    4. A wiring pigtail for the temperature probe (again at least just get 6" or so)

    Things that are nice to get but are harder to find or remove. For the mirrors here that have been / will be sold on this forum in the classifieds section these things usually won't be part of the deal as it takes a lot more time to get them etc.
    • A LONG pigtail from the mirror. The more of the wiring harness you can get the easier the entire swap will be. It takes more time however as you have to take a bunch of trim pieces off to successfully retrieve a large portion of the wiring harness.
    • Same thing for the temp probe. If you feel like tearing apart a large portion of the engine wiring harness to retrieve a few more feet of wire that's the best way but it's lots more difficult
    • The temperature probe mounting bracket. I say that this is optional because it's pretty easy to make your own from some sheet metal and tin snips. Sometimes the donor vehicle might have had a front end collision which would make retrieving this difficult.
    • The wire "guard" or "tunnel" I don't really know what this is called but it's a piece of plastic that is designed to run from the mirror to the headliner and clean up the appearance of the wire coming form the headliner to the mirror. These are sometimes hard to find. You might be able to get it from the dealership.
    • A weather-pack connector. It doesn't really matter where it's from. It's not necessary but I'd recommend a 2-3 pin connector. You'll see what this if for later.

    You'll also need some wire. (unless you pulled every inch of it from the donor vehicle) It's nice to color code it as it will help you keep things straight both now and down the road when you might be wondering "what is this wire for? :hmm:"

    • A T-20 Torx Driver
    • Phillips Screw driver
    • 7mm Socket/nut driver
    • Wiring supplies... (cutter, stripper, crimper, soldering iron, heat shrink, electrical tape, etc.)
    • All of your basic tools

    If you aren't sure how to pull the mirror from the donor vehicle after reading this guide about how to install one you should be able to remove one.

    Now it's time to start the installation:

    2. Remove the grill. This is necessary to install the temperature probe.

    Hopefully most of you know how to do this. It's not hard.
    1. Remove the 4 7mm screws that hold the top of the grill on and one that is down in the grill area right above the horn. A total of 5.
    2. Remove the parking lights
    3. Reach through and remove the side marker lights. Twist them a 1/4 turn and pull them out.
    4. Now the grill is held on by some clips. You should be able to reach in through the parking light holes are carefully free the grill from two of the 3 clips. The third is right in the middle. I usually pull the grill out just enough to reach down behind and pop that clip up. Be really careful as you wouldn't want to break anything by pulling too hard on the grill.

    Once the grill is removed you should have nice open access to where the temperature probe is going to be


    3. Mount the temperature probe:

    The temperature probe will mount right under the horn there and above the gray piece of plastic. The bracket that holds the probe is held on by that 7mm screw that you can see there in the gray area of plastic.

    If you have a stock bracket go ahead and mount it up now. I didn't pull the bracket for mine because it was already missing from one of the vehicles I pulled a mirror from and the other had been in a front end collision and so removing it would have been very difficult. I fabricated my own using some tin snips and some sheet metal. I sprayed it black so it wasn't a big shiny piece of galvanized sheet metal back there.



    4. Start to wire in the temperature probe.

    Splice in a nice long piece of wire to each of the leads if you have a short pigtail. I ran my wiring back down into the stock wire loom until I got behind the drivers parking light. I realized that it would be very difficult to fish it up through the stock loom at this point and I wasn't going to take that much time so I ran a new section of loom until I got it into the engine bay next to the ECM.


    There you can see it running back down into the stock loom.


    There is where I ran a new section of loom.

    Once I got the wire back into the engine bay area I dropped it back into the stock loom that runs along the inner drivers side fender. Follow it through this loom until you get near the fuse box.


    At this point I'd recommend using a weather pack connector. If you ever needed to remove your engine harness or remove your cab or just move some wires out of the way this is an easy way to save yourself some work down the road.

    If you have easy access to a wire for the reverse lights here would be a good place to bring it and place it through the weather pack connector too. I have a relay for my auxiliary back up lights mounted under the ECM so I ran my back up light wire from there. I believe that you can tap into it somewhere under the steering column as well.

    Now you need to get the wires through the firewall somehow. I already had a grommet with some other wires going through it so I squeezed these through that same grommet but you may have to drill a hole and install a grommet. I'd recommend fishing the wires through the grommet from the inside out. When you get them back into the engine bay splice them into the other side of the weather pack connector.


    Now that you have the temperature sensor wires inside the cab we can jump to installing the mirror and work backwards to the wires that we just ran. You are also welcome to put the grill back on at this point if you haven't already.

    5. Remove the old mirror.
    It's simply screwed into the windshield mount by a T-20 screw. Just remove that and the mirror will slide up and off.

    6. Remove trim pieces.

    At this point it's a good idea to remove the A-Pillar and the drivers sun visor. You'll need to take these down so that you can run the wires up the A-pillar and under the headliner.

    You may also want to remove the lower dash trim piece under the steering wheel. That will make it easier to run some of the wires. You probably don't need to remove this but it makes certain wires easier to get to. It is held on my 4 7mm screws along the bottom and a series of clips. Once the screws are gone you should be able to carefully pop it off.


    7. Build the mirror harness
    At this point you need to have a long harness for the mirror. Take your short pigtail and splice in a nice long piece of wire to each of the required wires. Try to make it long enough that they will reach all the way down the A-pillar and under the dash. I ended up splicing mine together right in the middle of the A-pillar and that led to me soldering above my dash :uhoh2: I'd try to avoid that in the future.

    The wires that you need are.

    If you've got a different mirror than the stock mirror you may have different color codes and you'll have to figure those out on your own.

    Once you've got a nice long harness for the mirror, Plug it into the back of the mirror and start to run it.

    Carefully pull down the edge of the head liner and push it up there as far as you can. Factory had the wires clipped to the ceiling with some of those plastic clips but I wasn't going to bother with those because I knew it would be a pain and I wasn't going to risk pulling my headliner down far enough to successfully clip them where they needed to go. I just tried to shove it up under the headliner as far as I could and make sure there weren't any bumps.

    Once you get it under the headliner all the way you can fish the wires down through the dash. There is a gap right at the bottom of the A-pillar that you should fish them down through.

    At this point you should have something like this

    8. Connect the wires.

    Now you will want to connect all the required wires together.

    For the pink power wire I installed a pin into one of the unused places in my interior fuse box and gave the mirror it's own fuse but I doubt that the mirror takes enough power to be an issue if you just splice into an existing switched power circuit. The pink wires under the dash should be switched power.

    For the ground you can tap into an existing ground or you can just make your own. I have a place where I've grounded several things before so I just placed my ground there.


    Now you just need to connect the temperature probe wires together and find a place to connect to the light green reverse lights wire (or ground it if you don't want that feature)

    9. Test it!

    Put the key in and turn it on. With some luck the mirror should light up and show you the temperature or the compass. Don't worry if the compass is not telling you the right direction right now it probably needs to be driven around the block to "get it's bearings." If it doesn't show the temperature when you press the temperature button but instead says OC that means that you have an open circuit somewhere. Go back and check the wiring for the temperature probe.

    I also shined a flashlight at the mirror to test the dimming function and then put it in reverse to see if that canceled the dimming function.

    Once you know that it is working you can button things back up.

    10. Put it back together:

    Push up on the headliner and make sure that it's velcroed up good.
    Reinstall your sun visor
    Wrap the wires in the A-Pillar with some loom tubing or just wrap them all the way down with electrical tape and then put the A-Pillar back on. It's a PITA so just take your time and be careful.
    Clean up any wiring under the dash that needs zip-tied out of the way or shortened etc. Then you can put the lower dash piece back on.

    If you have the little wire tunnel for the wires that go from the mirror to the headliner you can install it too.


    otherwise you will have to get creative or live with this

    11. Clean up your tools and enjoy your new mirror!
    95C1500, sewlow, -sin- and 2 others like this.
  2. JJZ71

    JJZ71 OBS for life

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    Jan 16, 2011
    I;m a little news there! If I hook up the power, ground & two temp sensor wires and I good to go with temp & compass - RIGHT?
  3. DRAGGIN95

    DRAGGIN95 Warranty Killer! Staff Member

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    Dec 5, 2009
    Antioch Arkansas
    Nice writeup man!
  4. borahshadow

    borahshadow I'm Awesome

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    Dec 4, 2010
    Almost... If you don't want the feature that disables the auto dim in when you are in reverse then you are supposed to ground the light green wire. Other than that you had it right. I hooked mine up, but according to stroker52 you need to ground it if you aren't going to hook it up.

  5. fun4me

    fun4me I'm Awesome

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    Feb 25, 2011
    Nice write up very detailed. I think it should be made a sticky. What about it mods?
  6. Devs93

    Devs93 OBS 4 EVA

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    Aug 16, 2010
    Shelbyville IN
    very nice write up one Q I was playing with one of the mirrors I have yesterday and pin 5 powers the auto dim on it wouldnt you want that hook up as well to use that feature? and green not sure wich pin was powering the compass I didnt have a 7 pin though so maybe thats the diff.

    This should be stickied
  7. 96twodoor

    96twodoor I dont own an OBS

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    Jan 11, 2011
    Bossier City Louisiana
    Very helpful, picked a mirror up today def gonna be using this ,
  8. borahshadow

    borahshadow I'm Awesome

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    Dec 4, 2010
    Pin 5? I wired it up exactly like I mentioned above and mine dims just fine. I just cut the wires going to pin 4 and pin 5. From my understanding of the wiring pinout that I got from stroker52 pin 4&5 are used to tell the outside mirrors to dim when the inside mirror dims. I'm not actually aware of any external mirrors for the GMT-400 that have the ability to dim.

    If your mirror has a 5 pin plug then it probably is wired up differently and pin 5 might be = pin 1. IDK I'm just guessing here.
  9. JollyGreen

    JollyGreen Metalworking Madman

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    Jun 21, 2011
    Tucson, AZ
    Excellent write-up. Can't wait to get a mirror.
  10. TruckinAin4Sissies

    TruckinAin4Sissies L.E.D. Whisperer

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    Aug 17, 2011
    In a Big-Rig
    Good luck on a sticky :/
    Pins 4&5 were in fact for auto-dimming mirrors. They came on some Esky/Hoes.
    You might've noticed them before, they have gold lenses.

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