Each mirror is ~7.8 ohms resistance. In cold weather they ohm out around 5.9 ohms. In a parallel circuit both mirrors will draw about ~4 amps. As the grids heat up the resistance rises and thus the current goes down. That's why its imperative to connect the mirror circuit to the rear defroster relay that time limits the grids. While low current, too much heat can shorten the life of the grids.
