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Where is the inside rear view mirror dimming control?

I bought a “new” used rear view mirror for my 1999 Lincoln Continental, because the auto dimming feature wasn’t working on the old one. It doesn’t work on the new one either. The “Workshop Manual” shows that there is a dial to set the control from off to positions I, II, and III, but I can’t find that dial anywhere. I would like to make sure that the control being set to off isn’t the reason it’s not working. I took apart the small box at the bottom of the mirror, but that only houses a circuit board. At least when I took that box apart and put it back together, the compass began working again . . . it works off and on when it wants to. The Workshop Manual basically says that when the auto dim doesn’t work, it either has a blown fuse (if that was the case the compass wouldn’t ever work), the control is set to off, or there is something wrong with the circuitry. I don’t have a way of checking the circuitry, so the only other thing I feel I might be able to do is make sure the control isn’t set to off. The only dash controls are turning the lights off and on, setting the headlights delay and controlling the panel dim and there’s no option for the rear view mirror on the onboard computer options. I’ve looked under the dash but don’t see anything that would apply. Any ideas? Thanks.

I don’t know the Lincoln but my Mercury has a button on the mirror itself. There is a light when the auto-dimmer & compass are on. Don’t know if that helps any.

Check to make sure the reverse signal lead is not on all of the time. The reverse signal overrides the mirror dimming circuit. Some mirrors have on/off push buttons on the front, some have a slide switch (that may even have max/min positions), and still others have no on/off switch at all.
The box at the bottom was just the electronics for the compass. The electronics for the mirror are inside the mirror housing.
Also, try unplugging the smaller connector to the mirror. (It goes to the outside mirror.) A fault with the side view mirror could keep the dimmer from working. If this is the case, the mirror will go back to working with the side mirror unplugged.

Are you sure that it has one? It doesn’t have a lever on the bottom of the mirror to switch it from tinted to clear?

Yes, mine has a button on the bottom of the mirror that’s suppose to switch it off and on, but nothing happens when I do that.

I don’t know what a reverse signal lead is. My mirror has an on/off button on the bottom of it, but it doesn’t work. The Workshop manual is showing a dial that I can’t find. Maybe it’s inside the mirror housing. I did unplug and replug the connector to the mirror, but it didn’t do anything. I tried to check all the wires to make sure none were loose. This is the inside rear view mirror I’m having trouble with, not the outside one. Thanks.

I don’t know what a reverse signal lead is. My mirror has an on/off button on the bottom of it, but it doesn’t work. The Workshop manual is showing a dial that I can’t find. Maybe it’s inside the mirror housing. I did unplug and replug the connector to the mirror, but it didn’t do anything. I tried to check all the wires to make sure none were loose. This is the inside rear view mirror I’m having trouble with, not the outside one. Thanks.

On some setups, the inside rear view dimming mirror controls the dimming of the outside mirror. In those setups, if the outside mirror shorts out, the inside mirror will fail too. That is what I was talking about.
Does your mirror have one, or two connectors plugged into it (coming from the top of the car)? This will determine if you have the dimming side view mirror option. You could have 1. A single three wire connector. 2. A single five wire connector, or 3. Two connectors.

There is a connection to the mirror to signal that the car is in reverse. When the car is in reverse, the mirror doesn’t dim. This is a safety feature. If this reverse signal is messed up, it can cause the mirror not to work.

Don’t put too much stock into the workshop manual that you have. The aftermarket manuals are often wrong on things like this. Even the factory manuals sometimes give information to applies to the wrong year models. The dial you are looking for doesn’t exist in your case. It did on some prior years, and was at the bottom front of the mirror.

I do have an auto dimming side view mirror and that seems to be working fine. It seems to only be the inside auto dimming function that isn’t working. The mirror has one connector plugged into the back of it. The mirror has 8 pins to receive the plug, but the plug only has 6 wires. I had assumed that the 2 not used were for map lights that some have, but mine doesn’t have them. The only control on the inside rear view mirror is the push button on the bottom that turns the auto dimming feature off and on. Also, there is a compass in the top right hand corner. The Workshop Manual shows the dial that I can’t find with an off and three settings, which I assume would adjust the sensitivity of when the auto dim feature was activated, but you may be right that it doesn’t exist. If it does, it’s well hidden. Thanks for your help.