Heated mirror question on 2016 2500HD WT

[GillyWI]

My brother in law picked this truck up for his slide in camper. He's retired and does this boondock camping (out west on federal land management land). Went from a 2006 GMC Sierra 1500 with a 4.3 & 4wd, to what he really needs to do this, a 3/4 ton, std cab long box 4wd. It's an off-lease with about 22K miles on it only.

So I put tow mirrors on it. Even tho a WT it has power heated mirrors on it and I got tow mirrors with these same features (non-GM mirrors). So, there is no defogger on the back window, when does the heated mirrors activate, does anyone know by chance?

 

Gilly

[J.H.2015LT]

The heated mirrors activate when you turn on the rear defroster.

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[SierraShorty]

My 2016 WT has heated mirrors and no rear defogger.  The mirrors come on with a switch located below the defroster switch.