the mirror will not cause this warning to illuminate. As one of the other post said check the rear side markers. Sometimes bulbs of different manufactures will cause this problem even if the bulbs look ok. By this I mean bulbs of different makes side to side installed the car. the fix is usually to replace all the bulbs with bulbs from the same package.(I'm talking about taillights). Only the exterior lights will turn the bulb warning light on. Clues to help diagnoses; key on, watch for warning light,Press brake pedal- Brake light bulb, parking light only on- parking light bulb, headlights same thing ,you get the picture. Good Luck,Brian