Except nobody in this thread using Port 2 and Port 8 has fried their mirror! And, the BlendMount website has some testimonials suggesting people doing what they recommended is fine. I'm pretty confident in the "gray wire theory."

I do apologize for my mental dyslexia -- I did understand that the RED wire is the + and goes into Port 2. And so it will.

Thanks again for keeping me straight.

If you got your Mirror Tap from BlendMount perhaps you could send them a note setting them straight?

 

I also appreciate your efforts BUT "my guess" is Bleadmount did not read a diagram wrong- they may have picked those Red and Black terminals they way they did not pick the terminals to tap for the C7. I'll explain:

Sometime in June 2020 before the C8 Vetteparts Online Video (mid July 2020) showing the mirror could be tapped using the Red and Black mirror wire terminals for Detector power I called Blendmount. I was not happy to be using my plan of the power receptacle under the passenger dash, when my C8 arrived. Called them because it was mentioned they were working on device to hold the detector under the mirror (as they did for the C7 etc.) Frankly was not interested in that device only the wiring. I talked to a Blendmount tech person who told me they did NOT define the terminals to tap in the C7, rather they relied on a customer telling them what worked. So they were no help and I was not going to mess with just probing with my VOM for + and - terminals, particularly because of the TV camera.

"My guess" is they, like most of us, used the Red to Red and Black to Black shown in their install video because of that 1st video and a number of us saying it worked fine. . As I have said, my detector has worked for ~14 months with no issues and no issues with the mirror. As the service manager and Corvette Tech said when they replaced my mirror they have seen that issue before on other cars (not related to mirror taps for detector power.) My detector was in place when I got the new mirror and power location has never changed in the 14 months since.

Appreciate you have looked at the wiring diagram and think that is not correct. Possible, BUT many of us are using those terminals just fine. And frankly although I see the GM bulletin I have not seen one forum post saying they had the issue!

I have no idea where Blendmount came up with the gray wire being an issue. Maybe they were in contact with GM?? Perhaps you can answer the question raised by Rapid Fred, what do you think would happen if the ground were connected to the gray wire?

 

Jerry, where you are confusing me is the part where you say you are using PIN2 and PIN8, and your mirror fried, mirror was replaced, and you are still using PIN2 and PIN8 (basically the same pins that blendmount recommends albeit with different #'s) for 14 months it has been good.

I don't see how having the mirror fried doesn't qualify as having a "problem". Yeah, it hasn't happened again in 14 months, but the mirror did fry though earlier correct?

 

^^^
First. I don't think my mirror issue had anything to do with the radar detector power. As I said, they occurred on different days and IF I taped the mirror first (still not sure, it was close timing) nothing happened until I saw the issue AFTER I came out of a store and got in my car. Frankly thought someone might have hit the mirror and looked for other damage. There was none. I googled and saw that dimming mirrors fail that way on other cars having zero to do with mirror power tapes. I have NOT changed the power taps from when I installed the detector. AND the Service Manger AND Corvette Tech who installed the new mirror said they had seen similar damage before on other cars and it's a defect issue NOT any mention of taping power. So again, I don't think my early problem is related. I have NOT seen any forum post where the issue occurred tied with the GM bulletin issue.

Second, yes my detector has been installed for 14 months the exact same way it's always been as I used that 1st Mid-July 2020 video showing Red to Red, Black to Black from C8 VetteParts Online. JUST what Blendmount shows on their install video, which is much more recent that when I taped the mirror as they did not have their mechanical mount device until recently and NEVER posted how to tap the C8 mirror until that was introduced. I believe most of us have used those terminals (note I avoid mentioning which number as that can cause confusion, it's simply Red to Red and Black to Black -not black/white- is what most of us have used.) It's what the pic in the July 2020 video showed and what I show in my PDF and used for my C8 received September 2, 2020.

I'm not changing what has worked for 14 months. There may be other terminals that work and ones that will screw up the mirror or TV camera but so far don't think there is evidence that Black to Black ground is one.

Just wondering what you think might happen if you tape the gray wire as Rapid Fred asked?

 

The grey wire from the pictures is in PIN9, which appears to be labeled as GY/WH in the schematic and shows that it is the switched positive power supply to the mirrors.
If you used that accidentally for your GND (slipped up and missed pin 8 nearby), I doubt the detector would work. Also don't understand how that would increase voltage to the mirrors UNLESS the mirrors aren't actually getting 12v! (the schematic does not say the mirrors are getting 12v, that is an assumption) What if the center mirror has a DC-DC converter in it and is feeding only +5V to the mirror when it wants to trigger the dimming function??? In that case, you would be pulling that +5V output high to +12v (minus some loss for the impedance in the detector). That might be enough to fry the mirror.

Given this supposed mirror issue with radar detectors, I think it is a safer method to connect to PIN 2 and PIN 5 which don't have direct connections to the mirrors.
It would be nice if GM would chime in and say something here, but given this is for installing radar detectors, my guess is they won't be helpful in this area.

Maybe you briefly inserted the pin wrong and then didn't notice the damage until the next day?

Anyway, this sounds like the most likely scenario to me, however the detector wouldn't likely function. So it would have to be something that happens during the install. It would be easy to prove this theory with a voltmeter (guess it would need to be dark and shine a flashlight into the mirror to trigger the photocell). If you see +3.3v or +5v at PIN9 then the issue would likely be settled.

So blendmount is probably correct stating not to use the grey wire as it might cause damage, they are just guilty of using the wrong pinout #'s. I think it would be advisable to avoid PIN8 and just use PIN5 instead, since that keeps you far away from the potential issue and it looks like the surrounding PIN4 and PIN10 are empty.

Special thanks to AndyBump for posting the schematics!

 

^^^
Thanks for the info. AndyBump supplies a lot of good input.

Decided to call Blendmount and talk to a tech person. He cleared up the issue. He said the reason they mention the Gray wire is someone had called them and one of the owners of the company called GM and was told connecting to the Gray wire can fry the dimming mirror! Wanted to be sure my PDF, which shows Red to Red and Black to Black was still accurate. Perhaps there is another that works but with many of us connected that way not ready to change.

I'll update my PDF with a "Be sure not to connect to the Gray Wire" when I get a chance.

I found a pic on the Net of another car with a similar mirror problem. As the Corvette Tech, who replaced mine 14 months ago said, he has seen similar issues on other cars.

Also posted a pic from a video on how it works.

 

Well, I wired my Radenso to the mirror a couple days ago. My fumble-fingers and tight tolerances forced me to use #2 and #8.

Working fine; no mirror problems. Day and night driving. SO much cleaner look for the elegant C8 interior.

Thanks again to everybody who has contributed to this thread.

 

I'm thinking of buying the Rodenso Pro M. How do you like the Rodenso, especially the K band filtering?

 

Educate yourself. This sight tells you what you need to know. NFI


https://www.vortexradar.com/best-radar-detectors/

 

I bought the Escort MAX3 earlier this year and am very happy with it in the C8.

 

I have an older XP and I am quite satisfied.

I note in the link Zormecteon provided a much newer technology Radenso does very well. At the time I bought mine, the XP was the best bang for the buck. Good filtering and GPS. I’d bet on them again if I felt I needed an upgrade…