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Compass/Temp/Auto dim mirror swap (detailed with lots-o-pics)

157024 Views 195 Replies 71 Participants Last post by  N8N
I saw this mod in someone elses post but the write up was vague and lacked the wiring diagram so I decided to do my own after finishing up my mirror swap.

The particular mirror you'll need to locate came on multiple GM models in different versions but the one your looking for is the 7 pin model most commonly found from 1995-2002 in Chevy and GMC trucks and full size SUV's also known as Gentex model number GNTX-177.

Besides the mirror itself, you'll need the 7 pin mirror connector w/ a small pigtail of wire, the ambient temperature sensor and sensor connector w/ a small pigtail of wire shown here;

The compass is part of the mirror itself but the temperature sensor is located on the front core support below the horn or on some of the newer models, right by the drivers side headlight. make sure to get at least 4-6" of pigtail for each connector to make wiring easier.

Once you've got those 4 items you need to decide how involved you want to make this and how much you care about your wiring job. Personally I overdo everything when it comes to wiring and this write up reflects that but there are quicker, cheaper and less involved ways to accomplish the same goal, i.e. using butt splices instead of solder joints and heat shrink, using split loom instead of braided expandable tubing etc.

You'll need the following items before you start but like I said, your list may differ from mine depending on what route you choose to wire your mirror in.

10ft - 20 gauge red stranded wire (power)
10ft - 20 gauge black stranded wire (ground)
10ft - 20 gauge black stranded wire (sensor ground)
10ft - 20 gauge green stranded wire (sensor power)
soldering iron (if soldering)
solder (or butt splices)
1/8", 1/4", 3/8" heat shrink tubing (or electrical tape)
PET braided expandable tubing (or split loom)
sheet metal screws
cable clamps in 1/4" or 3/8"
zip ties
electric drill
drill bit - 1 size smaller than sheet metal screws your using
sharpie (silver/black)
12v circuit tester
ring clamp - for ground wire
razor knife
wiring pliers
phillips screwdriver
torx - for mirror set screw

To start off with decide where you want to mount the temperature sensor, it will determine the length of your wiring run from the sensor to the mirror. You can put it anywhere there isn't a lot of heat and out of direct sunlight, just remember the further away from ambient heat (engine bay, radiator) you can place the sensor the more accurate it will be.

Next, you need to decide on which side of the windshield your going to run the power/ground/sensor wires to the mirror. Either side of your Jeep will work since there is switched power and ground on both sides of the dash, its more a matter of personal preference than anything.

Once you have your basic layout set its time to start on the mirror wiring. Start by stripping off the old covering so your left with a plug that and 7 wires;

Wiring for this particular mirror is as follows;

Your only going to be using wires 1, 2, 6 and 7 so remove wires 3, 4 and 5 from the connector. To de-pin the unused wires simply push down the retainer tab and pull the wire and pin out of the connector;

To start off, strip 1/2" of the insulation from the 4 remaining mirror plug wires and your 4 sections of new red/black/green wire then take your new lengths of wire and begin to wrap the stripped ends around each of the wires on the mirror connector like this;

Next solder the 4 lengths of wire together and then heat shrink them. Mark the end of either the black ground wire or the black wire from the temperature sensor so once its covered by the sleeving you can identify it and not mix it up with the other black wire when connecting everything, a silver sharpie works great for this step or use electrical tape etc;

Next, take a short section of the braided expandable tubing and slide it over all 4 wires. Its a pain to do but it leaves the harness seamless and very strong since any strain on the wires tightens up the sleeve and strengthens it. Once thats done slide a 1" or so piece of 3/8" heat shrink tubing over all 4 wires and the braided sleeving, close to the mirror connector but leaving a small bit of the wires sticking out of the braided sleeve, then shrink it down. Repeat this step for the end that goes behind the dash;

Locate the 2 wires (black and green) for the temperature sensor and crimp one male and one female insulated spade connector to each of them. This step isn't that important and they can be connected by any means you choose, I used polarized spades so they can't be connected wrong without cutting the ends off and re-crimping, doing so idiot proofs the harness for anyone working on the Jeep besides myself.

Next step is to build the wiring harness for the temperature sensor. On mine I made this part of the wiring harness seperate from the mirror harness so if I have to remove either of the harnesses in the future I don't have to tear everything apart.

Start by sliding a 1" long piece of 1/8" heat shrink over both of the wires on your sensor pigtail up to the plug itself and shrink it down;

Now take your 2 sections of new wire and strip 1/2" from each of the ends. Repeat this step on the 2 wires on your sensor pigtail then twist the 2 like colored wires together like you did with the harness for the mirror.

Solder the 2 joints, let it cool, then slide a 1" long piece of 1/16" heat shrink over your solder joints and shrink them;

Next measure out a piece of braided expandable tubing thats approx. 6" shorter than the length of your wiring harness and slide it over the wires leaving a 1/2" +/- gap at the end by the sensor plug. Slide a 1" long piece of 3/8" heat shrink over the sleeve to the end where the plug is. Make sure to cover the end of the braided sleeving and the wires protruding from the sleeve keeping it close as possible to the plug itself then shrink it over the sleeve and wires. Slide another piece of 3/8" heat shrink over the end with the bare green and black wire and the sleeve and shrink it down. This keeps the braided tubing from unraveling or fraying. Now crimp 1 male and 1 female insulated spade connector to each of the wires, doesn't matter which as long as they match the harness for the mirror Male to Female on each wire. Your end harness will look something like this;

Next, remove your factory Jeep mirror from the windshield. You'll need a torx to loosen the screw but I'm not sure which size since mine simply slid off even with the screw tightened up all the way. Slide your new mirror onto your factory Jeep mount and tighten it up till its snug.

Plug your mirror wiring harness connector into the back of the now mounted mirror then route it along the windshield frame and down behind the dash making sure to leave at least 2-3" slack at the mirror end for adjustment without putting strain on the wires. On mine I drilled some small holes and used 3/8" black plastic clamps and black metal screws to attach the cable to the windshield frame, running along the top towards the drivers side, then down the windshield pillar behind my flashlight mount and into the dash.

Another way to route the wire from the mirror to the dash is inside the windshield frame by drilling a hole above the mirror shown Here.

Lastly, if you have a newer wrangler you can just drill a small hole and run the wiring inside of your windshield trim;

Now find a good ground and using a ring connector ground the unmarked black wire to the body of the Jeep. I used the factory dash ground directly below the drivers side speaker;

Now break out your trusty circuit tester and find a switched 12v + power supply to hook up your mirror (+) to, make sure to use a 5amp inline fuse between your mirror (+) and whatever you tap into. On my setup I hooked the (+) red power wire of the mirror harness to the switched (+) I ran to my KC lights switch.

Once you have both the power and ground connected you can turn your ignition on and check to make sure your mirror powers up. If so, the compass and temperature gauge LCD window should power up and show a bunch of random characters. If the initial power up phase occurs the next thing you'll see is going to be "C" or "CAL" when you click the compass button and "OC" when you click the temperature button. Not to worry, the compass has to be calibrated and the temperature sensor will display "OC" for "open circuit" because you haven't connected the actual sensor yet. If the mirror powers up correctly then move onto the next step, if not you screwed up and need to check your connections or worse case you got a bad mirror.

Next step is to feed the sensor harness you built earlier through the firewall to the sensor mounting location you decided on. Slice a small hole in one of the firewall grommets and feed the wire through to whatever mounting point you chose, making sure you have a few feet of slack to route the wire around the engine bay.

Route your sensor harness along whatever path is shortest and most conventient then secure the harness with zip ties making sure it away from moving or sharp parts and then mount your temperature sensor. For this install I'm placing the sensor under the front left fender on the brace as there is already an existing hole that a 3/8" bolts fits through perfectly.

Once you have the sensor mounted up and the wiring ran and secured, power up the mirror by turning the ignition to the "Accessory" position and verify that your temperature function of the mirror reads an actual temperature and compare its reading to a thermometer. If the readout is horribly wrong or locked on 50 degrees, contact your GM dealer for a new one (p/n 15029274, $23) or return to the junkyard for a replacement, better yet hunt around and grab a spare when your there the first time just in case. Once thats done your ready to move on to setting and calibrating your new mirrors features.

Temperature display adjustment
To change the mirror temperature display between farenheit and celcius simply push and hold the "Temp" button until it flashes "f" or "c" on the side of the lcd, then press it again to change display modes. The mirror will switch back to temperature mode and now display in celcius or farenheit. The mirror also has a built in warning that will flash "ICE" every 6 seconds to alert of potential hazardous conditions when the temperature drops to 36f or 2c.

Auto-Dimming Switch Function
Hold "Temp" switch for 15 seconds to disable auto dimming and the green LED will go off, Repeat to enable auto dimming and the green led will come on.

Compass Variance
The mirror compass allows you to set the compass variance depending upon your location in North America. The mirror is set in zone 8 upon leaving the factory. It will be necessary to adjust the compass to compensate for compass variance if you live outside zone eight. Under certain circumstances, such a long distance cross-country trip, it will be necessary to adjust for compass variance. If you do not adjust your compass to account for compass variance, your compass can give false readings. To adjust for compass variance, do the following:

1. Find your current location on the map below.
2. Press and hold the COMP button for three seconds until a zone number appears in the display.
3. Press the COMP button on the bottom of the mirror until the new zone number appears in the display. After you stop pressing the button in, the display will show a compass direction within a few seconds.

US and Canadian variances;

Worldwide variances;

Compass calibration
Once the mirror is connected and powered up the compass display will read "C" or "CAL" because a long term loss of power allows the mirror to lose its setting of where north is and needs to be re-calibrated. If your mirror powers up and displays a heading, chances are its wrong and you need to force the mirror into calibration mode. To do this hold the "comp" button down for approximately 6-10 seconds or until it reads "C" or "CAL" then proceed to the next step.

If your compass is displaying "C" or "CAL", simply drive in a tight circle (in a parking lot for example) under five miles an hour until a compass heading is displayed. Typically this should take less than three complete turns. If this doesn't work, drive normally and over the course of your route a heading should display.
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Discussion Starter · #2 ·
Temperature sensor addendum

After cruising the junk yards for mirror swap parts I decided to add this little addendum to my original write up regarding the temperature sensors.

I noticed after looking at certain vehicles and doing some research I found out that GM used 2 different types of temp sensors and 2 separate types of sensor plugs and the 2 different styles are not interchangeable regardless of what the dealer parts monkey says his computer shows.

In this image you'll notice 2 of the sensors are identical with the exception of the mounting brackets and 1 is completely different. The two that look the same are the same and will interchange with each other so if you need/want one style or the other your fine. The third style, "C" is not interchangeable due to the plug being different, but using that style plug from the get go allows you to use the newer and cheaper air temperature sensor. People on the various GM forums swear that the new style is more reliable and less prone to false readings but I used the older style, "A", in my setup and its dead on with the thermometers I have at home, as are the rest of the older style sensors I tested.

Notice in this picture the green plug in the center, "2". It is the only plug that fits the newer style temperature sensor "C" from the previous picture due to the seperating notch the arrow points to. This sensor can be used just fine and was most common in newer vehicles that had the temperature readout displayed on the climate control instead of the mirror. Also notice in the picture that the wire color and gauge on the connectors are different and vary slightly from green and black to green and yellow. From my tests as long as you connect green to green and black to whatever is the odd color your good to go.

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1,098 Posts
Discussion Starter · #4 ·
Way to go. Excellent write-up. I personally don't need that mod but was just checking out my old stomping ground and having a look around. I've read plenty of write-ups and have done a few myself but yours is the best. :thumbsup: :cheers2:
Thanks! I spent a lot of time on it so its nice to hear its actually informative. :thumbsup:

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1,098 Posts
Discussion Starter · #6 ·
I did it in a little less than 3 hrs start to finish but I spent a bunch of time figuring out the wiring, If I hadn't I could have done it in an hr or so. If you feel like doing it and have a problem just post up and myself or others will chime in and help you out. As long as you can measure wire and use a tester light your good to go.

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1,098 Posts
Discussion Starter · #11 ·
Nice job on the wiring. This is a mod that's on my shortlist, however I want a mirror that also has Homelink buttons.

Another option for the inside wiring, for those of us who have older TJ's without the plastic trim, is to actually run it inside the windshield frame. Someone on here did it (Oman Jeep maybe?) and looked really good.

He drilled a small hole in the bottom of the frame, right above the mirror. With the windshield folded forward, the wire was able to be snaked through so it came out by the hinge.
I saw a bunch of the homelink ones in the yard and thought about swapping that in it but they wanted $80 for all the parts, most likely because they'd have to dig into the dash for the brain. If I could find one @ pick a part I'd be all over it tho, not having the garage door opener stuck to the visor would be a major plus!

Ya, it was Oman's write up where he drilled the holes and snaked it through the windshield frame. I thought about going that route as well and I still may do that but my plan was to upgrade to the newer style windshield trim since it cleans up the interior a bit.

I'll add a link to Omans write up for those who want to drill and run it inside the frame, thanks for reminding me! :thumbsup:

Where are the temp sensors usually hiding on the junk yard cars? Good write up BTW. Might do this soon.
The temp sensors are located behind the grill usually clipped to the core support directly below the horn. Updated write up to reflect that.

That is sooo sweet! Good job man. I appreciate the offering to help. I'm gonna have to give this a shot this weekend. I was lookin so long on this site and others for a good write up. Mad you! :cheers2:
Once you get started you'll be surprised how easy it is. I am going to be doing the swap into 3 more Jeeps so let me know if you want/need more detailed pics of anything.

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Discussion Starter · #13 ·
I hope you're right! I don't wanna be swearin your name. :) Do you know this, when I go to the junk yard do they pull off the equipment I need or do I have to hunt this stuff down and pull it?
I went to the local U-Pull-It and got the temp sensor and plug and to an actual wrecking yard for the mirror and plug. Call up some local wrecking yards in your area and ask for a 98 Tahoe compass/temperature mirror and see what they will charge. Most places have no clue that they are over $400 from the dealer and will let them go cheap. Its also going to be your best bet for finding one with the least amount of driving around and searching.

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Discussion Starter · #19 ·
Thanks for clarifying! No wonder why I never heard of it, there are not in my area. Do you think I could get them from Autozone, Checker or Advance???
They go by many names, u-pull-it, pick-a-part, they are just a wrecking yard where you pay a couple bucks to go in the yard and pull the parts off the cars yourself instead of having the yard do it for you. If you can find the mirror and plug just ask them if you can have them pull the sensor for you at the same time. The place I went for my first setup let me go out in their yard with one of the parts pullers and show him what I needed

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Discussion Starter · #54 ·
I picked up the factory mirror and sensor. I went to install it this weekend, and the plug on the dash is not there. The sensor plug is where it is supposed to be. The PO of the TJ had an alarm system installed at the dealer. I wonder if they used that plug or wires for it? Does anyone know where the plug/wires originate from? If I could find that maybe I could determine a solution. Of course my fall back is to find the other plug and just wire it in.
I'm not absolutely sure they all have the plug under the dash cover strip. Mine is an 02 and it didn't have one hence the reason I used the Tahoe version. I'll see what i can find in terms of a wiring diagram for the factory plug and add it to the write up. Worst case scenario its really only 4 wires you have to add to make it work; power and ground and the temp sensor wiring.

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Discussion Starter · #144 ·
Man this is a cool idea, was thinking overhead console. Saw this is alright, got mirror from wrecking yard $25, ordered plug connector and sensor $16 apiece. Gonna like this in my 2000 XJ
Wow! I cant believe this thread is this long now! Good idea on the mirror in a different model of Jeep, I actually re-did this mod on my GC 5.9 so I can display compass/temp on my mirror and leave my overhead console on the mpg setting.... helps me avoid getting 5mpg on premium from mashing my foot down constantly! :D
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