Upgrading the Review Mirror to Include Homelink, Alarm, Auto-dim, and Compass

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I’ve been reading all about this issue with using newer mirrors with the Homelink, not being compatible with factory alarm setups, etc… great information was provided by everyone including this post (http://forums.bimmerforums.com/forum…mirror+pin+out) and still I wondered…

[me wondering – imagine cloud thought above my head]: “why can’t we just take the ‘alarm’ part of the old mirror out, insert it into the new mirror case, feed it power and get the best of both worlds?”

So i got to crackin cases… you gotta be careful when doing this. I was able to practice on my original one because I knew I wasn’t going to keep it! Use a plastic putty knife from your local hardware store. There are two main releases/catches on the top and bottom. They are about 6 inches apart and something like an inch or so from each edge. If you use the plastic putty knife like the kind in the picture
You should be able to wiggle the edge of it into the separation at least enough to see which side of the mirror’s seam has the catch. The trick is to slip the plastic knife in there enough to see which side the rest of the knife edge needs to go into, then carefully slide the knife along the seam into the opening until it cracks open, hopefully not cracking the catches. Once you get one side open using this technique, it will be more obvious how to open up the other catches.

I present to you this: This is my 1995 CSi mirror taken apart:

You will note the “alarm” portion of the mirror screwed down on the left with a yellow antenna wire along the bottom. The ‘switch’ for something hanging down in the middle of the mirror and to the right, the opening for the photo sensitive cell that drives the whole dimming feature (I think). Also note the way the wires are separated for some reason – not sure if that’s even relevant…

Next take a look at the innerds of a non-compass, E36 mirror with Homelink:

The IC board looks much more sophisticated of course – it’s like 10 years newer. The Homelink unit is to the left, pretty much self contained, only needs power and ground to make it work, yet there’s 10 wires total feeding the 10-pin connector, which is identical, by the way, to my 1995 CSi mirror except that the CSi plug only has 9 wires and obviously the wire to pin assignments are a little different. (yes, I know I need to re-solder/fasten that ground connector for the dimming feature to the outside of the mirror (black loose wire). I will take care of that…

shows my 95 mirror with the alarm receiver portion removed and the internal wires/connector spread apart to help identify their colors. And finally,

shows the new E36 mirror’s internal connector and wire colors.

Now I know that in Frankie’s post about plugging in the newer mirror to the older socket involved switching a couple wires (3 to be exact). He said:

original 1 (brown) to new 10 (ground)
original 2 (blue) to new 1 (reverse signal)
original 3 (yellow/red) to new 3 (power)


So apparently, since there’s so many more wires going on in the 95′ mirror, I’m assuming they have something to do with feeding the alarm signals that it needs? (when I tried to just unhook the 95′ mirror from the car, the alarm sounded and wouldn’t go off unless I re-attached the mirror and hit the unlock on the key fob!)

My goal is to ‘integrate’ the previous mirror’s alarm module, into the new mirror’s chassis so I have Homelink AND the alarm receiver in the new mirror.

So here’s the ask to the gurus:

How do I need to re-wire this thing to allow me to take the alarm module, and mount it inside the new mirror and still feed everything the appropriate signals?

Thank you in advance for any and all help you can provide!

Taylor in Cardiff

Additional Info: This morning I managed to find this at (http://www.baso.no/load.asp?id=85) which appears to be the pinouts for an E39’s electrochromic mirror (my newer mirror with Homelink). Looks like pins 4,5,6,7 are used to send dimming signals to the side rearview mirrors. Do any of the E31s have this?

Now if I could just find the same information about ALL the pinouts of the E31 alarm mirror, then we can try matching them up, splice them together, and see what happens!




About the Author:

I am an 8 Series nut. In 2009 I restored a '92 850i to peak condition and subsequently sold it - which left me depressed. So I embarked on catching my White Whale: this '95 850CSi Chassis #CD00166. I’m opinionated and swear constantly, but I have friends in spite of myself. I am funnier than my wife realizes. Please tell her. Cheers!


  1. Taylor  August 5, 2010

    I should finally fix the auto dim and the problem of my alarm module blocking the photocell sensor so I picked up some photocells at radio shack this afternoon and dismantled the mirror again. Below is the circuit board.

    There are two photocells. One for detecting light coming from the front (the one that’s blocked) and one facing to the back of the car detecting headlights behind me.

    I want to simply take this new photocell and wire it into the existing solder joint with enough wire to reach around the alarm module. Then I’ll be right as rain.

    However, this being a newer circuit board, it’s micro soldered, not easy to just splice in a new one so I don’t want to make any mistakes and so I have a few questions.

    As you can see I’m using red arrows to point to where I THINK I need to splice in the new photocell. Yet the factory photocell is mounted on 4 points. But it looks like only two of those points (the red arrows) are electrical. The other two appear to be just mount points.

    In the 2nd photo you can see the same micro photocell but from the opposite side. This is the one that faces to the rear of the car. Same sort of thing, two mount points, two electrical connections.

    Before I solder, does anybody know electrically what the capacitors would do as pointed out by the green arrows and why would they (at least in appearance) be at “the end point” of the electrical connection?

    I hope I’m explaining my question well enough but it looks like they are capacitors (C13, C15, C for capacitor versus R for resistor) I’m assuming, right?

    Do you think it should be safe to carefully solder my new photocell where the red arrows are pointing? And what effect would an extra say six inches of thin wire lead have on the resistance produced by the photocell? Do I need to be concerned about that? Does using a larger photocell help overcome additional resistance by having the extra wires or would that have no effect?

  2. Taylor  August 9, 2010

    Finally some success!

    OK so here we go… Mounted the alarm module on the right side of the new mirror and pulled the old mirror’s wiring harness through. Because of the way I had to mount the alarm module, I had to actually extend the length of the wiring so it could be fed through to the car’s plug.

    Then I wired up like Frankie said, using the new mirror’s wire connector. I removed the other six, unnecessary wires from that plug as well.

    Putting car in reverse correctly un-darkens the mirror, the alarm module is fed a constant power signal and receives my keyfob inputs, and the Homelink works perfectly.

    Only problem is because of where I had to add the alarm module, it blocks the light signal from the back of the mirror (facing forward of the car). That results in a constantly darkened mirror, even though reverse temporarily undarkens the mirror.

    Now I have to just figure out how to ‘feed’ that light diode with natural light from the outside of the mirror. I am thinking of mounting some sort of redirection ‘tube’ of clear plastic that would be long enough to go around the alarm module and into the back side of the mirror where the diode is.

    Anyone got any clever ideas for that?

  3. Taylor  August 10, 2010

    So I sampled the voltage off the old mirror and this is the story.

    OK so I’m no electrical expert so please bear with me. Objective is to take the remote control module out of the old mirror, install it into the new Homelink mirror (this one came from an E39), and splice the wiring appropriately so everything works. The challenge is harder because the old and new wiring colors are not the same (except for maybe ground) and the new mirror does not appear to have any provision for the remote (pin 2 is absent). Add to that the lack of pin out assignments ANYWHERE for the old mirror and my very much less than complete knowledge of how to read electrical schematics and I’ve got a real big challenge!

    At first I thought why not just move the old remote module and glass over to the new case that has the Homelink and be done with it. And of course, the problem there is the new case is wider than the old mirror glass so DRAT! That would have been the simplest way. It’s possible then to maybe take out the Homelink module, cut some holes in the old mirror case and feed it power from the old harness but the cases being so different, with the manual switch thingy in the old mirror (which I would have to remove), and me not having a stamp cutter, and me not being so good with an Exacto blade, I’m leaving that for a last resort.

    My current approach is, if I were able to take the wiring harness from the old mirror out (probably have to cut and re-splice the wires) and transfer it to the new mirror, then the remote module would work plug and play. I just would have to figure out how to properly feed the new mirror’s power and signal requirements from the old wire harness. Since I DO have pin assignments/colors and schematics for the new mirror (at least I *think* I do) from http://www.baso.no/load.asp?id=85 I’m thinking maybe that would be the best approach.

    Problem is this: It’s a one way ticket. Unless I know what I’m doing BEFORE I do it, when I hook up the batteries, the car will bitch at me that the remote isn’t right and the alarm will sound just like it did when I simply removed the old mirror. So I need some help from people more electrically knowledgeable than me to give me the best chance at getting it right before I start cutting. I don’t have a spare mirror. I am hoping the voltage readings might shed some light on the picture of what’s going on inside these wires, at least enough to signal some confirmation of their purpose. If we can swing this conversion, I will fully document it for all to do it themselves.

    Here are my observations about the voltage readings (using a typical volt meter) on all the mirror pins against ground on pin 10. These were taken without the electrochromic mirror plugged in, just the case’s 10-pin connector (with the remote module) into the receptacle. I took measurements when the car was unlocked and locked, off and in ACC, and also monitored any pins that had a voltage change when actually pressing the lock/unlock/arm button on the key to try to determine all wires’ behavior.

    Pins and voltage readings from the 1995 E31 mirror with remote receiver integrated and the switch for activating the dimming feature.

    PIN color unlocked locked comment
    1 Grey 0 0 goes to 0.5 when ACC is on and 11.89 when in reverse
    2 Red 11.89 11.89
    3 Yellow 0.14 0.14 goes to 11.41 when ACC is on
    4 White 0 0
    5 Green 0 0 quick jump to ~6 volts (& back to 0) when car is locked
    6 Black 0 0 quick jump to ~6 volts (& back to 0) when car is locked
    7 Blue 10.65 10.64
    8 Violet 11.31 11.13 cycles between 11.32 & 11.31 on regular basis
    9 Pink 11.15 11.13
    10 Brown ground

    Posts say that in order to work, one of these pins needs to provide power to the mirror at all times so that it can detect when the key fob is pushed. That looks like pin #2 but could also be pin 7, 8, or 9. Since pin 8 appears to cycle on a tiny draw every second or so, my suspicion was that THAT was the alarm receiver module pulsing some signal out?

    According to the Electrical Manual for the 95 E31, the old mirror has pin 3 coming from fuse 18 and pin 1 coming from the front power distribution box on fuse 17 and is associated with the reverse/backup light signal. What’s with that? Are the mirrors supposed to Undim when you’re in reverse? Pin 1 on the old and new mirror are the same. Also according to the schematic from http://www.baso.no/load.asp?id=85 for the new mirror, pin 2 is an Infrared remote control signal, even though in MY new mirror, there is nothing there. Obviously pin 2 in the old mirror would not mate up like pin 1 because it’s voltage is consistently on – unless you guys think that actually might be accurate, a pin 2 to pin 2 match. See, this is where I know only enough to get into trouble!

    Pin 3 is yellow in the old mirror and pin 3 in the new mirror is supposed to be hot in run/start. Pin 8 is violet in the old mirror, has constant voltage in all modes and is the one with the cycling behavior. Pin 8 in the new mirror is supposedly hot all the time. If the fact it pulses in voltage is irrelevant, then pin 8 old to new would be a matchup. Pin 9 is reportedly the LED control for the alarm which is redundant in the form of the center console light but in the old mirror it has constant voltage so that is probably not a match.

    Also the thing I’m trying to wrap my head around is the difference in the auto-dim stuff between the two mirrors. According to the manual: “The mirror gradually darkens to reduce glare whenever the ignition key is in position 2. As glare subsides, the mirror returns to its normal position. Position 0 = the mirror is switched off. Position 1: the mirror is placed in anti-glare position. When put in reverse, the mirror switches to its normal position.”

    So I guess that just means that no matter which position the manual switch on the mirror is in, putting the car in reverse defeats it. And the fact the new mirror has no such manual switch simply means it’s always on, yes? That being the case, perhaps its pin 8 (with the pulsing) that should feed the power to the new mirror’s photocell?

    So I’m left with pins 4, 5, 6, and 7. Pin 4 doesn’t appear to be jack. No voltage in any situation. Pin 5 does a quick jump to about 6 volts when you push the remote button to lock the car then goes back to 0 so this pin is sending some signal out from the module to tell the alarm to arm?
    Pin 6 has the same behavior as pin 5 so what the heck?
    Pin 7 has a pretty constant voltage

    In the schematic of the newer mirror, pins 4 & 5 are paired and pins 7 & 8 are paired. Both sets go to connector X302 and X303 respectively. I suspect they lead to the side mirrors to enable the dimming feature in them when the central mirror detects glare; a feature I’m pretty sure the E31 never came with and I don’t see any similar electrochromic edging in the two side mirrors to indicate they’re capable of dimming. So I’m assuming (in the absence of verification of where connectors X302 and X303 actually go, that’s what they do in E39s (where the new mirror came from). Anyone got an E39 Electrical Manual they can send me or verify from?

    So sorry for the long story but I wanted to put my observations and thoughts out there to see if anyone with more knowledge about these mirrors and their electrical properties could help. Perhaps I’m just over thinking it but if, based on this information and your own, the old harness could just be transferred to the new case and mirror glass, and I can correctly splice in the power/signals to the new mirror’s connector and wires – then life would be good. And we may have solved the Homelink/Alarm mirror integration question once and for all.


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