1999 GMC Sierra replacing side mirrors

Hello and thanks for donating

If your vehicle has heated side mirrors, there should be a symbol on the mirror's glass with a small picture of a side mirror with heat waves coming from it. The rear defroster button will turn on the side mirror heater as well. You can replace the side mirrors with heat enabled side mirrors even if your vehicle is not equipped with the heat, although they will probably be more expensive than the non heat mirrors.