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Thread: Be Seen !! ...and put that rear fog light to use...as a brake light

  1. #1
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    Exclamation Be Seen !! ...and put that rear fog light to use...as a brake light

    I don't believe in the search function on this site, because everyone recommends it and I'm not swayed by peer pressure.

    So if there's a write-up similar to this already, ban me.

    I was driving behind an E39 yesterday, and noticed that the brakelight section of our taillights isn't very big, and really isn't too visible either. ...so I got to thinking, I remember seeing a blank socket on my taillights that is reserved for a rear fog light, which is not commonly found on E39's in the US.



    Why not make it another brake light?



    Here's how you can do this simple mod:

    First, you'll have to remove your taillights. Start out by unplugging and removing the covers that carry the bulbs. Notice the empty socket on the bottom row. This is reserved for the factory rear fog light bulb.



    Next, remove the lenses. There's 4 8mm nuts holding each lens to the car.



    If there is no hole for that fog bulb in the lens, you'll need to drill one.



    I used a 1" hole saw bit for mine.



    An air compressor will come in handy to blow any plastic shavings out of the lenses once they have been drilled.

    Now take a look at your bulbs. On the OEM lights, the grounds are all connected through a network of metal rails, so all you will need to do is jump the positive rails for the fog lights to the ones for the brake lights. I used a small piece of 18 gauge wire and soldered directly to the positive rails. The ones you will want to connect are highlighted below.



    Once they are connected, just pop in some bulbs (they use the same 21w bulbs that the brake lights use). Put everything back together and you're done.


    Last edited by defaz; 12-22-2008 at 02:00 AM.

  2. #2
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    soooo... now ur rear fog light is a brake light-

    great idea-

    i can't stand ppl that drive with their rear fogs on...

    I guess all those people should do this mod instead.

  3. #3
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    Pretty cool idea actually... Are there any issues with the OBC reporting any bulb failures?
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  4. #4
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    Quote Originally Posted by Asharus View Post
    Pretty cool idea actually... Are there any issues with the OBC reporting any bulb failures?
    nope, the only issue I can see would be that the OBC wouldnt tell you if only one of the bulbs is out. You'd have to have both burnt out on one side before it reports a bulb failure.

  5. #5
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    looks damn good to me, nice work

  6. #6
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    Beautiful! Great alternative to putting rear fogs in there, I might just go do that wednesday


  7. #7
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    I like...

    I was actually thinking about that the other day. neat mod. maybe if I get really bored.
    Wade

  8. #8
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    Damn, you stole my idea.

    Kudos!

  9. #9
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    Question: based on the circuitry, I'm assuming that the bulbs are in series, rather than in parallel. This seems like it would put too little current going through the bulbs, since they're 21W bulbs.
    Or do they not have a common ground before the power source?
    Also, do you have a clearer, higher res pic of the leads that you soldered a wire between? I'd need something better than that before I'd feel confident doing this myself

    Thanks in advance, and looks great!
    --Charlie

    2009 MCS 6 speed


  10. #10
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    we do it on our Audis as well,

    If someone is tailgating you on the highway, hit the switch and theyll back off w/o you having to brake

  11. #11
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    i wish i could do this, but i have no soldering tool!

  12. #12
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    another question: do you think this could be done with quick disconnects instead of soldering?
    --Charlie

    2009 MCS 6 speed


  13. #13
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    Quote Originally Posted by cliffhanger407 View Post
    Question: based on the circuitry, I'm assuming that the bulbs are in series, rather than in parallel. This seems like it would put too little current going through the bulbs, since they're 21W bulbs.
    Or do they not have a common ground before the power source?
    All the bulbs in the taillight share a ground, and I only tied the positives of the 2 brake bulbs together so they're wired in parallel... right? They seem to be pretty bright, I guess that picture with only the left side done can be used to compare the before/after output.

    I'll get the high res pic tonight...

  14. #14
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    Quote Originally Posted by defaz View Post
    All the bulbs in the taillight share a ground, and I only tied the positives of the 2 brake bulbs together so they're wired in parallel... right? They seem to be pretty bright, I guess that picture with only the left side done can be used to compare the before/after output.

    I'll get the high res pic tonight...
    danke
    That would make them in parallel if they have a common ground, yes.
    --Charlie

    2009 MCS 6 speed


  15. #15
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    Quote Originally Posted by cliffhanger407 View Post
    another question: do you think this could be done with quick disconnects instead of soldering?
    On my last taillights (aftermarket) I was able to just jump a wire between 2 pins in the female side of the plug, but the factory ones dont have a pin in the plug unless the car came with the option, so soldering on the inside was my only option...

  16. #16
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    Quote Originally Posted by defaz View Post
    On my last taillights (aftermarket) I was able to just jump a wire between 2 pins in the female side of the plug, but the factory ones dont have a pin in the plug unless the car came with the option, so soldering on the inside was my only option...
    makes sense. thanks for the info.
    --Charlie

    2009 MCS 6 speed


  17. #17
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    ok gonna sound silly, is there any way (even just for the moment) to do this mod with out soldering (i have depo tails)... if that helps

  18. #18
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    the only way to do it without soldering is if your depos have a plug coming out of the light housing with some wires attached... On my last aftermarkets I was able to cut the lead going to the fog bulb and attach it with the standard brake bulb and it worked just fine...

    ...But if those depo's have the plates with the metal rails like the factory ones, you're stuck having to solder unfortunately, unless you can get some sort of pin for the factory side of the plug where the fog light wires would have been..

  19. #19
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    Quote Originally Posted by defaz View Post
    , I remember seeing a blank socket on my taillights that is reserved for a rear fog light, which if I recall correctly, only like 22 total E39s are equpiied with worldwide.
    Sorry to say this but all Eurospec cars have rear foglights
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  20. #20
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    Quote Originally Posted by tsaros View Post
    Sorry to say this but all Eurospec cars have rear foglights
    This is going to sound stupid, but...what's the purpose of rear foglights? So people can see you clearly as they drive up behind you? Or are they for backing up in dense fog? Seems like if the fog's thick enough that you need rear foglights for either of those purposes, you shouldn't be driving anyways.

  21. #21
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    Quote Originally Posted by rocketwagon View Post
    This is going to sound stupid, but...what's the purpose of rear foglights? So people can see you clearly as they drive up behind you? Or are they for backing up in dense fog? Seems like if the fog's thick enough that you need rear foglights for either of those purposes, you shouldn't be driving anyways.

    1.So people can see you clearly as they drive up behind you is the purpose, sometimes the fog hits quite fast and the fog lights gives you a little extra distance to be seen in.
    Im not saying its used daily, but i have used them a few times when you have not seen the road more then 2ft in front of you.

    Your point about not driving under thoose conditions is valid, but if you do get caught they are quite good to have.

    The problem with thick fog might be a non-issue in some parts of the world and there it would make perfect sense to use it as a extra brakelight.
    535d -08
    unmodded and almost fully loaded .

  22. #22
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    The depos use the same assembly in the back, you dont actually replace that part, however it makes this mod easier since the fog light hole is already pre-drilled.
    2011 WRX Limited w/ Nav, Tach Motor Works & JR Tuned - Stage 2+ ~ 306 awhp 328 ft/lbs @ 19psi
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  23. #23
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    Quote Originally Posted by rocketwagon View Post
    This is going to sound stupid, but...what's the purpose of rear foglights? So people can see you clearly as they drive up behind you? Or are they for backing up in dense fog? Seems like if the fog's thick enough that you need rear foglights for either of those purposes, you shouldn't be driving anyways.
    Rear foglights are useful not only in fog, but also during heavy rainfall. I remember driving from Texas to NY and there was HEAVY rainfall. My bro was driving in front of me in his Porsche Boxter and I remember he turned the rear foglight on and I was able to see him in the distance.

    On Porsches, only the driver's side foglight turns on. The same thing on Mercedes-Benz. I remember thinking what's up with Benzes always driving around with broken taillights (brake light stuck on) and mentioned it to my other bro that drives a Benz. He corrected me and told me that they are the fog lights. I noticed on his light switch that one click (pull) turns the front fogs on, and two clicks turns the rear on. Most benz drivers probably dont realize that they are turning on their rears as well.

    On Audis I noticed that the rear fogs are on both sides (passenger and driver). Does anyone know if the BMWs in Europe have them on both sides or just one side?
    2011 WRX Limited w/ Nav, Tach Motor Works & JR Tuned - Stage 2+ ~ 306 awhp 328 ft/lbs @ 19psi
    AEM Intake, Process West TMIC, GFB Respons BOV, Invidia Q300 Turboback, Grimmspeed EBCS
    AEM Wideband & Boost Gauges, SMY Cluster, SPT Short Throw Shifter/Bushing, 30% Tint

  24. #24
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    Quote Originally Posted by Asharus View Post
    Does anyone know if the BMWs in Europe have them on both sides or just one side?
    We get them on both sides.
    535d -08
    unmodded and almost fully loaded .

  25. #25
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    Here's a better picture of the 2 rails that need to be connected. This is the Right side taillight, and the Left is a mirror of this one. Just connect the 2 highlighted rails and that's it...

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