Take the mirrors back off and check the wiring. You have a wire pinched or there is a short in the mirrors somewhere. If you check the wiring coming out of the mirrors going to the plugs and don't see anything then its probably shorted internal to the mirror somewhere. To check for an internal short on the mirror itself, get a multi-meter and set it to the ohms setting and with the mirror off the truck, put one probe in one slot on the plug on the mirror and the other on one of the mirror mounting studs or any part of the mirror that is metal and see what it reads. It should be infinite ohms or open. If it reads low (50 ohms or less, probably closer to 0) then that is your short. Repeat this with each slot in the plug. None of them should read shorted, they should all read open. If you find that the short is internal to the mirror then return them.