Retrofitting Auto Dim Rearview Mirror

Bullseye07 · July 29, 2019

So it kinda amazes me that autodimming rearview mirrors are not a standard option these days.

Since it’s not, I’d like to retrofit one in on my 2018 LT. Those of you that have done this mod, where did you get your mirrors at? And about what did you spend?

From what I’ve read pgamboa makes a wiring harness for this, so just need to find a reliable source for a mirror. The search function is giving me troubles.

While I’m at it, does anyone know of someone that makes a rearview mirror relocate bracket? I have one on my Tacoma that essentially moves the mirror all the way to the roof and it’s surprising how much it improves your field of view.

Thanks for any info.

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zikronix · July 29, 2019

i picked my mirror up on ebay. They are basically all the same. at the same time i did the power fold and auto dimming for my side mirrors too. I only wanted to be under the dash once because its a giant pain in the ass.

pgamboa · July 29, 2019

This is the part # to what I personally used on mine.

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F362662345963

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Bullseye07 · July 29, 2019

Thanks Phil. I’ll probably be hitting you up for some wiring on one of these pretty soon too.

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pgamboa · July 30, 2019

Thanks Phil. I’ll probably be hitting you up for some wiring on one of these pretty soon too.

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Sounds good!

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Nasty · July 30, 2019

Phil made my swap super easy. It took me 20 minutes maybe. Hardest parts was pulling down the overhead console

mmmikkke · July 30, 2019

Note that:

1. Most car manufacturers buy their auto-dimming mirrors from GENTEX. Most of the mirrors available on ebay (new or used) are GENTEX mirrors.

2. WT trucks (trucks with Work Truck trim level) do not have a compass as equipped from the factory.

3. WT trucks do not have an auto-dimming inside rear-view mirror as equipped from the factory. Instead they have an old-style manual-dimming prism-based mirror which unfortunately is a few inches out of the reach of most drivers including myself. It requires an extreme stretch--while driving--to flip the tab on the bottom of the mirror to change from un-dimmed to dimmed and vice versa. Not very safe!

I replaced my factory mirror with a GENTEX GNTX-455 mirror with built in digital compass. It fits the existing factory glued-on mirror mount and works as expected. The compass dims automatically at night.

https://www.ebay.com/itm/Gentex-Auto-Dimming-Universal-Rear-View-Mirror-with-Compass-GNTX-455/173319918081

Adding an auto dimming GENTEX mirror WITH COMPASS solves 4 problems with GM trucks with WT option levels:

1. It eliminates the image echo at night when the dash lights are reflected multiple times by the rear window and mirror in the manual mirror image. With the LCD based GENTEX mirrors, there is no prism and therefore the reflection of the dash lights only occurs once. (WT owners will know what I am talking about.) It makes it much easier to look-past the dash lights reflection when backing-up at night.

2. You can add a compass since otherwise in a WT, you have no compass.

3. There are no On-Star buttons on this mirror model (GENTEX GNTX-455) and that fits the WT perfectly since it doesn't have On-Star vehicle tracking.

4. The out-of-reach problem is solved because the mirror dims automatically. (The initial mirror position adjustment will still require a stretch but this can be done while parked.)

You can add a compass-equipped GENTEX mirror to any GM truck since the compass is entirely contained inside the mirror and does not require any additional wiring beyond what is required to use a GENTEX mirror that does NOT have a compass. All you need is a switched 12V feed (IGN or ACC) and a ground. The outside temperature display is not needed--or wanted--since it's already available in the RPO IO3 radio display and a temperature signal may not be available in the overhead console.

It takes 15 - 30 seconds for the GENTEX mirror to transition from daylight mode to dimmed mode, or from dimmed mode to daylight mode at 70 degrees Fahrenheit. Upscale GM trucks provide a backing-up signal to un-dim an otherwise dimmed GENTEX mirror if backing-up at night where lights and glare are present. But since the mirror is so slow to change modes, most people are already done backing-up before the undimmed mirror can assist them. I did not bother to provide a backing-up electrical signal to the mirror to enable this ridiculous feature.

The GENTEX 455 has only one button and it is to toggle the dimming feature on/off. That is a more logical way to un-dim the mirror for those few times you will ever want to un-dim the mirror for backing-up. Even then, you will have to wait 15 - 30 seconds before the mirror regains full reflectivity.

Bullseye07 · July 30, 2019

Note that:

1. Most car manufacturers buy their auto-dimming mirrors from GENTEX. Most of the mirrors available on ebay (new or used) are GENTEX mirrors.

2. WT trucks (trucks with Work Truck trim level) do not have a compass as equipped from the factory.

3. WT trucks do not have an auto-dimming inside rear-view mirror as equipped from the factory. Instead they have an old-style manual-dimming prism-based mirror which unfortunately is a few inches out of the reach of most drivers including myself. It requires an extreme stretch--while driving--to flip the tab on the bottom of the mirror to change from un-dimmed to dimmed and vice versa. Not very safe!

I replaced my factory mirror with a GENTEX GNTX-455 mirror with built in digital compass. It fits the existing factory glued-on mirror mount and works as expected. The compass dims automatically at night.

https://www.ebay.com/itm/Gentex-Auto-Dimming-Universal-Rear-View-Mirror-with-Compass-GNTX-455/173319918081

Adding an auto dimming GENTEX mirror WITH COMPASS solves 4 problems with GM trucks with WT option levels:

1. It eliminates the image echo at night when the dash lights are reflected multiple times by the rear window and mirror in the manual mirror image. With the LCD based GENTEX mirrors, there is no prism and therefore the reflection of the dash lights only occurs once. (WT owners will know what I am talking about.) It makes it much easier to look-past the dash lights reflection when backing-up at night.

2. You can add a compass since otherwise in a WT, you have no compass.

3. There are no On-Star buttons on this mirror model (GENTEX GNTX-455) and that fits the WT perfectly since it doesn't have On-Star vehicle tracking.

4. The out-of-reach problem is solved because the mirror dims automatically. (The initial mirror position adjustment will still require a stretch but this can be done while parked.)

You can add a compass-equipped GENTEX mirror to any GM truck since the compass is entirely contained inside the mirror and does not require any additional wiring beyond what is required to use a GENTEX mirror that does NOT have a compass. All you need is a switched 12V feed (IGN or ACC) and a ground. The outside temperature display is not needed--or wanted--since it's already available in the RPO IO3 radio display and a temperature signal may not be available in the overhead console.

It takes 15 - 30 seconds for the GENTEX mirror to transition from daylight mode to dimmed mode, or from dimmed mode to daylight mode at 70 degrees Fahrenheit. Upscale GM trucks provide a backing-up signal to un-dim an otherwise dimmed GENTEX mirror if backing-up at night where lights and glare are present. But since the mirror is so slow to change modes, most people are already done backing-up before the undimmed mirror can assist them. I did not bother to provide a backing-up electrical signal to the mirror to enable this ridiculous feature.

The GENTEX 455 has only one button and it is to toggle the dimming feature on/off. That is a more logical way to un-dim the mirror for those few times you will ever want to un-dim the mirror for backing-up. Even then, you will have to wait 15 - 30 seconds before the mirror regains full reflectivity.