GM Service Manual Online
For 1990-2009 cars only

With the ignition switch in the ON position, ignition positive voltage is supplied to the inside rearview mirror. When the transmission is placed in the REVERSE position, battery positive voltage is supplied to the reverse input circuit of the inside rearview mirror. The inside rearview mirror will gradually change to a clear state as a result of the reverse input. Ground to the inside rearview mirror is supplied by G103.