There are only two wires that run from the fuse box/chassis through the rubber boot into the driver’s side door for mirror MOVEMENT. The power wire (black/yellow) from pin G1 of the fuse box (12V with ignition switch ON) goes straight to the mirror control switch in the driver’s door. A ground wire (brown) plugs into the pin on the grounding ring above the fuse box, and goes straight to the driver’s side mirror. At the mirror, the ground wire splits in two and also provides ground for the defroster in the glass. Power for the defroster (white/green) does not go through the switch but straight to the mirror glass for defrost. That circuit is powered by the rear window defroster switch. Mirror defrost comes on whenever the rear window defrost is switched on.
Three power wires run from the mirror switch to the mirror: black, blue, and white. The power for up/down and left/right are the same two wires, the black and blue ones. The mirror switch just reverses polarity for reverse direction. There is only ONE motor in the mirror. The additional white positive wire from the switch operates a clutch in the mirror that makes it change axis from left/right to up/down. Whenever you move the switch for up/down motion the white wire goes hot or "ON." It stays cold or "OFF" when operating the mirror left/right. All these wires are part of the drivers side mirror harness, harness #1.
Three power wires that are part of harness #1 run to the passenger mirror from the mirror switch in the driver’s door. They are blue/black, black, and white. They run through the rubber boot on the driver’s side door jamb and out under the dash near the fuse box. There they plug into the under-dash harness (#2) in which there is an additional brown ground wire for the passenger side mirror. That wire also grounds on the same ground ring above the fuse box. Harness #2 runs all the way across the vehicle under the dash and plugs into harness #3 behind the glove box. That harness runs through the black boot on the passenger door jamb and into the passenger door. The power for up/down and left/right are the same two wires, the blue/black and black ones. The switch just reverses polarity for reverse direction. There is only ONE motor in the mirror. The additional white positive wire from the switch operates a clutch in the mirror that makes it change axis from left/right to up/down. Whenever you move the switch for up/down motion the white wire goes hot or "on." It stays cold or "off" when operating the mirror left/right. Again, the white/green wire is for mirror glass defrosting and has nothing to do with power mirror MOVEMENT.
The whole system
What is unusual about this system and throws people for a loop is that the black and white wires are COMMON to both mirrors. The black wire may be positive 12V or ground at any given time depending on switch position, up/down, left/right. This will be so at BOTH mirrors simultaneously. But only ONE mirror, the one selected by rotating the switch to “L” or “R,” will get positive 12V or ground on the BLUE or BLUE/BLACK wire, left and right mirror, respectively.
That is not the most confusing part. Anytime EITHER mirror is moved up/down, BOTH mirrors get power to the clutch via the white wire. So, both clutches click. That is a crummy thing about this system. I think both clutches being powered creates a bit of a power drain in the system, and one reason these systems commonly need higher-than-usual power to operate. Even when all is perfect, it is not unusual for the system to require more than 12V to operate well (engine running and revved up). That is why on some vehicles the mirrors work fine when driving down the road, but not when sitting still with the engine not running.
For a visual reference, refer to Robert Bentley manual page 97.184 for the circuit diagram of this system.