# Rear fog info ... headed in the right direction?



## Kaz (Dec 21, 2001)

OK, so I decided to sit down and spend a few minutes trying to figure out this rear fog business. I started out by paging through the Bentley to figure out the pinouts of the light control module.

Long story short, it appears Pin49 runs the rear fogs directly. This position in the wiring harness in my car is unused.

Here are the new questions:

-Will the US Light Control Module send power out of Pin49 when the appropriate signal is sent from the control switch?
-Which control switch unit to get? There is the one that has the headlight height adjust knob. OK, I don't need or want it but would it work? The adjuster motors are there but I coulda sworn that knob was only for halogen cars. :dunno:


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## Terry Kennedy (Sep 21, 2002)

Kaz said:


> *Here are the new questions:*


I have a light control module on order which claims to be the right part (there are a zillion versions, and I need the one with the auto-position (11:00) on the headlight switch, but without the leveling knob for manual-leveling Xenons). I'm away at Amanda's again, so I won't get to confirm the correct part has arrived until I'm back in a week or so.

My goal is to use the rear fog button to activate an electronic deer whistle I need to add (there's a dead deer every couple miles between my place and Amanda's, and at 800 miles each way that's a lot of deer and I'm nervous). The deer whistle folks cover the insurance deductible on a deer collision, so it's well worth it.

Anyway, I'd like to share information. One thing I'd like to have is the rear fog indicator in the instrument cluster showing whether the whistle is on or not.


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## Kaz (Dec 21, 2001)

I don't know about using the switch to activate other stuff. I'd like to say it might be possible by using that same pin 49 to trigger a relay and operate whatever else you want to use. I think the indicator light won't be a problem, as the communication between the control module and the instrument cluster is through a K-bus signal, so as long as the control module is sending power out the pin, the light will go on. It might look for a load on that pin as well so having the control panel connected with nothing on pin 49 might not work.

What I can say with a fair amount of certainty is that you won't be able to use the panel's button directly (bypassing the control module) as it seems like the control panel and control module only send logic information, not actual switching signals, between each other.


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## Terry Kennedy (Sep 21, 2002)

Kaz said:


> *I don't know about using the switch to activate other stuff. I'd like to say it might be possible by using that same pin 49 to trigger a relay and operate whatever else you want to use.*


The whistle only pulls a few milliamps (despite all the hooplah, it's just a tuned piezo chirper in a tube).



> *I think the indicator light won't be a problem, as the communication between the control module and the instrument cluster is through a K-bus signal, so as long as the control module is sending power out the pin, the light will go on. It might look for a load on that pin as well so having the control panel connected with nothing on pin 49 might not work.*


I'm not sure the lamp in the instrument cluster is stuffed in US models - we'll have to see when we get our parts.



> *What I can say with a fair amount of certainty is that you won't be able to use the panel's button directly (bypassing the control module) as it seems like the control panel and control module only send logic information, not actual switching signals, between each other. *


Well, this might be a bit of a bummer. I have the whole assembly coming, so I can see what is involved. But replacing the module will introduce a stored vital data miscompare and the tamper light will come on in the instrument cluster (VIN and odometer data is redundant between the light control module and the instrument cluster) and I'd rather not have to go to the dealer and get it reset. It also raises a fault that will appear on the diagnostic computer.

Since there is a switch in the button (which the USA control module probably isn't expecting) I figured I could lift the traces on the PC board and run my own wires to the switch, making it completely independent of the control module, if the US control module doesn't recognize that switch.


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## Kaz (Dec 21, 2001)

The rear fog indicator light is there and does turn on. Run the dash diag mode as covered in the Bentley and see for yourself.  

You are correct about the consequences of changing the control module. The control panel pops off very easily and a short detachable ribbon cable connects it to the control module so if I were you I'd just swap the panel first.

I think the series of tests would involve something like this:

-swap control panel only
-hit rear fog switch, see if dash light comes on
-Also, check pin49 for +12v

If all these check out, then we have a winner on our hands. The control module appears to run the rear fogs directly, and the stock bulbs are 21w so a measly piezo device shouldn't be a load problem at all, though because its not a physical switch in the module (if you look in it its filled with what look like power transistors and some other stuff) it might not be enough of a load to switch the circuit and you may need to add some extra resistance.

What did the entire module cost? I've read somewhere on the order of $170 for the whole thing and $40 for just the control panel.


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## Patrick (Dec 23, 2001)

I am not trying to be a smart-ass!  BUT, what is the reason why US-spec BMWs do not have rear fog lights?

Second question: why do so many people want to DIY retrofit these?

I have rear fog lights and I do use them from time to time, especially when there is fog or snowy conditions. However, I just don't understand what the buzz is all about!

Tell me and I will shutup.  

Patrick


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## Killer Junior (Dec 21, 2002)

Kaz said:


> *OK, so I decided to sit down and spend a few minutes trying to figure out this rear fog business. I started out by paging through the Bentley to figure out the pinouts of the light control module.
> 
> Long story short, it appears Pin49 runs the rear fogs directly. This position in the wiring harness in my car is unused.
> 
> ...


Where'd you get the rear fog kit? How much?


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## ·clyde· (Dec 26, 2001)

Patrick 520iAT said:


> *I am not trying to be a smart-ass!  BUT, what is the reason why US-spec BMWs do not have rear fog lights?
> *


Probably because the typical US driver can't be trusted to use them appropriately. Remember that a significant number of American drivers leave their fog lights on all the time.


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## The HACK (Dec 19, 2001)

[email protected] said:


> *Probably because the typical US driver can't be trusted to use them appropriately. Remember that a significant number of American drivers leave their fog lights on all the time. *


I'd like a rear foglight (and stick a higher wattage bulb there) just to 1) piss off tailgaters and 2) annoy idiots with their foglights on, so they can see how stoopid and rediculous their car looks from the rear, all the time.


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## bmw325 (Dec 19, 2001)

Kaz said:


> *The rear fog indicator light is there and does turn on. Run the dash diag mode as covered in the Bentley and see for yourself.
> 
> You are correct about the consequences of changing the control module. The control panel pops off very easily and a short detachable ribbon cable connects it to the control module so if I were you I'd just swap the panel first.
> 
> ...


So Kaz-

Does this mean that by just swapping the control panel and adding the rear fog light, it will work?! That's very cool. Do US cars have the socket for the rear foglight, or do you need to somehow wire that up? I wonder if any coding changes need to be made to the central body computer.


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## Ausfahrt (May 3, 2002)

robg said:


> *So Kaz-
> 
> Does this mean that by just swapping the control panel and adding the rear fog light, it will work?! That's very cool. Do US cars have the socket for the rear foglight, or do you need to somehow wire that up? I wonder if any coding changes need to be made to the central body computer. *


By just buying the switch and the rear foglights will not make the rear foglight work. The US cars are missing a wire that goes from the front of the vehicle somewhere to the rear foglights. I had the people at County Line BMW show me the wire that is missing on the US cars and he highlighted the for me. Unfortunatly I did not get the paper he printed for me. You can call County line in CT and talk to Americo the service mechanic and verify this. Unless your going to fabricate this or buy the wire from BMW that's the only way it's going to work. Here's my switch.


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## Ausfahrt (May 3, 2002)

Ausfahrt said:


> *By just buying the switch and the rear foglights will not make the rear foglight work. The US cars are missing a wire that goes from the front of the vehicle somewhere to the rear foglights. I had the people at County Line BMW show me the wire that is missing on the US cars and he highlighted the for me. Unfortunatly I did not get the paper he printed for me. You can call County line in CT and talk to Americo the service mechanic and verify this. Unless your going to fabricate this or buy the wire from BMW that's the only way it's going to work. Here's my switch. *


Here's one more pic of the switch.


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## Terry Kennedy (Sep 21, 2002)

Ausfahrt said:


> *Unless your going to fabricate this or buy the wire from BMW that's the only way it's going to work. *


Right - we know from previous posts that the US models don't have that wire in the harness, nor do they have the socket for the rear fog lamp (it is a molded-over piece of plastic in the light housing).

For my project, that doesn't matter as I need the switched power up at the front of the car.


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## Ausfahrt (May 3, 2002)

Terry Kennedy said:


> *Right - we know from previous posts that the US models don't have that wire in the harness, nor do they have the socket for the rear fog lamp (it is a molded-over piece of plastic in the light housing).
> 
> For my project, that doesn't matter as I need the switched power up at the front of the car. *


Yes, I'm just clarifying some things with robg or other people so he doesn't get the wrong impression on this retrofit. It's not like the OBC retrofit where you buy the parts and get it on the DIS to make it work.


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## Kaz (Dec 21, 2001)

For those asking the 'how can I do this' questions, please re-read my (and Terry's) early posts.

This is a project in the making. I've poked around the Fanatics archives and have seen numerous threads on this but so far nothing more than people buying and installing the control panel. I haven't seen anyone else mention that pin49 on the module is what appears to run it.

IF I'm right, and IF this works, the minimum required parts will be the following:

-Control Panel appropriate for your car (halogens or xenons)
-connector socket insert to fit the open position on the 54pin connector on the back of the light control module
-wire
-connector socket insert to fit the open position on the ??pin connector on the reverse light fixture
-reverse light fixture(s) with sockets for fogs
-bulbs

As for why BMW leaves em out of US cars (Volvos, Audis and MBs have them), I don't know.

And I want them for their intended purpose (it doesn't get foggy often but when it does it can be really bad), but also for the same reason HACK wants it. Too many foolios here tailgate or drive with their highs on that I want a way to alert (annoy) them.


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## Ausfahrt (May 3, 2002)

Kaz said:


> *also for the same reason HACK wants it. Too many foolios here tailgate or drive with their highs on that I want a way to alert (annoy) them. *


This is why BMW wont install rear fog's on BMW:tsk: Just put a flood light in the rear if soemone comes near you turn the light on and blind them so they can wreck.


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## Killer Junior (Dec 21, 2002)

*Re: Re: Rear fog info ... headed in the right direction?*



Killer Junior said:


> *Where'd you get the rear fog kit? How much? *


 :dunno:


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## dasWolf (Jan 4, 2002)

Kaz,
I don't know if you've seen the info at this E39 site. It may be of some help for you with the E46.

http://www.bmwtips.com/

"Tips & Tricks" scroll to "Lights" Item "8. BMW Rear Fog Lights"

http://www.bmwtips.com/tipsntricks/Rear Fog Lights_files/Rear Fog Lights.htm

http://www.bmwtips.com/tipsntricks/rear fog light updates/2001_rear_fog_install_updates.htm


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## Kaz (Dec 21, 2001)

dasWolf said:


> *Kaz,
> I don't know if you've seen the info at this E39 site. It may be of some help for you with the E46.
> *


Yeah, I did come across this earlier on. Its a great site and I'd like to see (put together??) something like this for E46s.

The general idea is identical (run wire from control module to back of car, change switch, change/modify bulb carrier) but because the parts are totally different it's gonna be a discovery process.


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## Terry Kennedy (Sep 21, 2002)

Kaz said:


> *it's gonna be a discovery process. *


Well, I have good progress to report - I picked up the control module at the dealer - 61 31 6 919 835 (see footnote) and took the switch assembly off the front and installed it in the car. Operation of the previously-equipped lights is normal, and pushing the rear fog button does illuminate the rear fog indicator on the instrument cluster - no MODIC coding needed. The pre-existing front fogs make a "click" when turned on/off, which is a relay lurking somewhere in the car's innards, while the rear fog doesn't do that. I don't know if there is a missing relay or if the module has the power to control the single rear fog without the relay (it doesn't matter for my application as the deer whistle I want to control only pulls a few milliamps).

One other observation - the rear fog instrument indicator only illuminates (and thus, I assume the rear fog lamp will only light) when either the headlight switch is in the "on" position or when it is in "auto" and it is dark enough to auto turn on the headlights. This would limit the switch's use as a general purpose switch.

I haven't yet started work on wiring the whistle to the control module - I just got home at midnight and installed the switch panel as a quick hack.

Note: I disconnected the battery negative terminal and waited 5 minutes before pulling the control module out of the dash. This may be overkill, but better safe than sorry...

Footnote: the part number I gave above is specific to E46's with bi-xenons, auto-on headlights (is this standard these days, or part of PP?) and auto-leveling headlights (standard in the US, but not in parts of Europe - you could easily wind up with a panel with two wheels - one for console light brightness and one for headlight angle) if you're not careful. There _should_ be a way to just order the switch faceplate and not the whole control module, but I haven't found it - it isn't in the parts CD and there isn't a part number on the faceplate itself (there is one on the circuit board, but you also need the various plastic parts). Lastly, remember that if you swap the whole control module, you will trigger a tamper alarm for the VIN and odometer reading, and you'll need to visit your dealer to have it reset.


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