well swap in your heated mirrors first. wiring is simple. there should be 2 or 3 wires. i have seen both types

type 1 (2 wires) one is negative and the other is positive switched via defroster OR ignition through a switch so it will only heat during winter
type 2 (3 wires) one negative, one positive, one is the jumper selectable trigger. with the trigger you can allow a negative pulse or posiive pulse to actuvate heated mirrors.

most are type 1 and if its type one. you will look for a YELLOW/WHITE (neg trigger) for rear defrost. this is a 10 minute trigger.