I doubt there is any possible simple hookup like an after market camera hookup feeding a video monitor. My gen1 had the picture in the Nav but my '11 Tahoe had the monitor mirror. The signal fed by the camera likely requires further video processing through the separate Nav module that processes the signal and feeds the signal along with the input from the steering wheel for the rear projection lines controlled through the DIC and ultrasonic bumper modules to the radio head, a mirror screen may require a separate module containing the hardware for the LCD display, a proprietary radio head and/or dealer reflash for radio head....the mirror contains a video display but may not be like a stand alone monitor, just the display screen driven by a separate module or the properly flashed radio head. A stand alone test monitor may work, but absent the programming and/or the module to process the signal the LCD screen won't. Further the wiring feeds in the mirror harness depend upon the stock mirror for the vehicle, whether a flip mirror with on star buttons, a self dimming mirror with onstar buttons or a LCD display, self dimming with OnStar.....factory camera display mirror has a 1/0 button which is for the self dimming feature without LCD display, but is a push and hold to turn on or turn off the LCD display for those with cameras. Eg. On a harness with a stock flip mirror there is one active power feed pin in the harness for OnStar, but not for the pin powering the self dimming function......been there, done that, replacing an OnStar flip mirror with a self dimming mirror OnStar mirror requires running a separate positive feed from an ignition source to feed the power pin for the self dimming feature
Actually surprised the dealer even attempted to locate a mirror pinout. It is irrelevant to them, all they want to know or care about is to replace the mirror, driver module, camera or radio head until the mess works and could care less about the specific pinouts in the mirror.
Current Chevys -'19 Silverado RST;'18 Malibu LT Redline;'18 Traverse Premier Redline<br /><br />Previous Chevys:16 Silverado LT;16 Malibu LT2;'17 Impala;'16 MalibuLT;'15 Camaro LS;'15 Traverse; '13,'12 and '07 Avalanche LTs; '11 Tahoe LT; '13 &'11 Malibu LTs; '08 Trailblazer;'06 Colorado WT..... Chrysler era.....'80 Citation;'75 Impala;'72 Chevelle;'69 Camaro R/T;'65 Impala SS;'62 Nova