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Author Topic: Simple reroute DRLs to Foglights mod (for HID users)  (Read 4647 times)

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Offline TomatoSoup

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Simple reroute DRLs to Foglights mod (for HID users)
« on: November 02, 2012, 04:43:58 PM »
Now that I have my HID projector headlights in place, I don't want to have them on at full brightness all the time because of the DRLs. Crappa has a solution that he came up with on the BB, but it involved extra external wiring and relays and I thought there MUST be an easier way, so I studied the schematics and came up with the following.  It involves modifying two relays and keeps all the wiring inside the underhood fusebox.  Plus, it's easily and quickly reversible by just replacing the modified relays. 

NOTE: The method below causes the fog lights to be used as DRLs.  It also (!) retains the ability to switch on the fogs, even if the DRLs aren't on.

First the caveat.  I take NO RESPONSIBILITY for any damage resulting to your car when following these instructions and/or doing this modification.  On your own head be it!

So what we're going to do here is simply break the output of the DRL relay and just cross-link it to the coil pin of the fog light relay, as shown in this modified schematic. Thus, no changes need to be made to the car's wiring harnesses:
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OK, so a couple of ways to do this.  In my case, I bought a pair of Omron relays from Digikey <this> for just $4 each plus $3 postage - or probably available at similar cost from your local parts store.  I then took them apart and internally wired (later).  However, a perfectly good option is to cut off the pin from your existing DRL relay and solder the cross-link wire to the correct pin of your fog light relay.  This photo shows the two relays (inverted, obviously, since they are upside-down) with the green line showing how to solder the wire and which relay pin to cut off:
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Here's how I rewired the Omron relays, should you buy them and want to do it this way.  First unclip and pull off the relay shell/cases, then drill a small hole in the top corner of the shells  to allow the wire to exit (see the picture to see which corners to drill!). 

Then, for the DRL relay, cut the innards and solder the wire as shown (NOTE: this works for this Omron relay ONLY, other manufacturer's relays may be different internally, and certainly the ones in my car from the factory were NOT modifiable internally as the contacts/wiring are enclosed/hidden inside - in which case, you would need to use the external method above) [whew!]:

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Now feed the wire through the two relay cases (don't forget to do this before soldering!!), then solder the fog light relay like this:

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Finally, now you have your relays wired together, simply go to your car and open the fusebox (below).  Unplug the foglight relay #54 and the DRL relay #48.  Replace them with the modded ones.  NOTE THE ORIENTATION -- any other connection could blow a fuse or even fry your BCM! To confirm, see the red-sharpie arrows on the relays, pointing to the big red Positive terminal on the fusebox.

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Close up the fusebox and you're done!  Reversing it is a simple matter of replacing the two relays with unmodified ones.

Hope this helps anybody who has HIDs and doesn't want them on all the time :)
« Last Edit: September 05, 2017, 02:06:27 PM by TomatoSoup »
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Offline Va_Sky

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Re: Simple reroute DRLs to Foglights mod (for HID users)
« Reply #1 on: November 02, 2012, 07:14:20 PM »
Nice mod idea Soup.... By the way that wire type looks very familiar....  :censor: That's all I'm sayin bout that......  :poke:
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Offline TomatoSoup

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Re: Simple reroute DRLs to Foglights mod (for HID users)
« Reply #2 on: November 02, 2012, 10:25:30 PM »
Nice mod idea Soup.... By the way that wire type looks very familiar....  :censor: That's all I'm sayin bout that......  :poke:
Well, not sure what you mean, but it probably isn't what you think.  It's actually some super-high quality wire I  had from my old job... stranded, silver-plated and teflon insulated!  Just happened to have a thick-enough gauge, yet thin enough insulation to fit past the relay innards :)
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Offline Carbon Sky

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Re: Simple reroute DRLs to Foglights mod (for HID users)
« Reply #3 on: November 02, 2012, 10:45:24 PM »
I refuse to be one of those people who think it's 'cool' to drive around with their fogs on all the time.

So this rewire will make the fogs behave like DRLs, while disabling them as foglights?  I'm just a little confused because I'm pretty sure that's what you just described, but you just also said you don't want to drive around with fog lights on all the time.

Offline TomatoSoup

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Re: Simple reroute DRLs to Foglights mod (for HID users)
« Reply #4 on: November 03, 2012, 09:34:25 AM »
So this rewire will make the fogs behave like DRLs, while disabling them as foglights?  I'm just a little confused because I'm pretty sure that's what you just described, but you just also said you don't want to drive around with fog lights on all the time.
Yes, it will make fogs turn on as DRLs.  The Fogs will NOT be on when the headlights are on however.

If you really still want to keep the Fogs available at all times, implement it per the method in the last main para and solder the wire to (and keep) the fog relay.
"That is my theory, it is mine, and belongs to me and I own it, and what it is too." (Monty Python)

Offline Carbon Sky

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Re: Simple reroute DRLs to Foglights mod (for HID users)
« Reply #5 on: November 04, 2012, 01:10:01 AM »
Yes, it will make fogs turn on as DRLs.  The Fogs will NOT be on when the headlights are on however.

If you really still want to keep the Fogs available at all times, implement it per the method in the last main para and solder the wire to (and keep) the fog relay.

Thanks for doing the work.

Personally, I have BARELY ever used my foglights.  Like you, I pretty much consider them useless.  If it's daytime and nice weather, I run with no lights on.  If it's crappy out, raining/foggy, but still light out, I will switch to the first position on the stalk, and may or may not turn on the foglights, depending on how concerned I am about being seen in poor visibility.  I like it much better this way as the rear lights will be on as a result, even though the headlights are off.

Since I don't drive througha lot of heavy rain and thick fog, I rarely use the foglights.  And at night, when I have the 55W HIDs on, it's flippin bright.  Especially since I went with 4300K, and am not losing any lumens by going up in the temp range.  I do a lot of driving on rural roads with 80km/h limits, with large stretches without street lighting and compared to other cars around me, I look like a UFO with the light I throw forward.  So needless to say, the foglights would be useless for me under those conditions.  From the driver's seat, I cant tell if they are on at all.

Offline TomatoSoup

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Re: Simple reroute DRLs to Foglights mod (for HID users)
« Reply #6 on: November 04, 2012, 05:45:53 PM »
Aggh!  :gaah:

OK, I made a minor boo-boo with the first version of this mod, that I only realised today when I had my car out.  The old method works it's just that it routes the DRL voltage to the fogs, which meant the fogs are only on half-bright!   :censor:  Given the d*mn things aren't that bright to begin with, I went back to the drawing board.  Good news is the new version isn't much more difficult, but it does mean that you HAVE to modify both relays, but then it retains the fod light override function (ability to turn on the fogs even if DRLs are off).

Anyway, apologies.  The initial post in this thread has now been modified to the new method.  Thanks.
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Offline silverfox90

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Re: Simple reroute DRLs to Foglights mod (for HID users)
« Reply #7 on: January 09, 2013, 07:35:35 PM »
Decided to try this today, since I retrofitted my headlights and never use the fogs. I tried both methods shown above and cannot get the fogs working as the drls. I can manually turn the fogs on or off, but they do not come on as the headlight drls used to. I now have it wired as in the first picture with the drl relay post cut and wire soldered to that point and the fog relay is wired as shown in the second method, drilled through the top and soldered on the inside. I do notice that with the drl relay soldered on the exterior the relay does not completely seat flush in the fuse box. Any suggestions?
« Last Edit: January 09, 2013, 07:43:08 PM by silverfox90 »
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Offline TomatoSoup

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Re: Simple reroute DRLs to Foglights mod (for HID users)
« Reply #8 on: January 09, 2013, 11:15:33 PM »
First and foremost... are you testing with the handbrake on?  I shan't say how I know but it has (ahem) been suggested - I mean I've heard... Oh OK, I was effed by this situation too!  If the handbrake is on, the DRLs go out.  So when testing and parked and you naturally have the brake on, it's a real P*sser to find out that that was the problem all along! 

Let the handbrake off and check that first and then report back.

Oh, before I forget, you ARE doing this outside in daylight, right? You need the auto headlights to be ON.
« Last Edit: January 10, 2013, 12:02:41 AM by TomatoSoup »
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Offline silverfox90

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Re: Simple reroute DRLs to Foglights mod (for HID users)
« Reply #9 on: January 10, 2013, 03:44:12 AM »
Bingo! I never thought to try that. I spent all that time thinking I somehow managed to screw up one of the more simple electrical mods. Thank you very much for the troubleshooting advice and for taking the time to share this with us! I have some yellow bulbs on the way so now the fogs will be drl, but still functional if needed.
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Offline Helios

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Re: Simple reroute DRLs to Foglights mod (for HID users)
« Reply #10 on: December 17, 2013, 10:17:29 PM »
Did this mod today in conjunction with my 6000k HID install. Thanks, TS. Unfortunately, I have one HID bulb that is intermittent (i already troubleshot and know the bulb is bad) and have requested a replacement be sent. Also, my fogs are intermittent as well, but I've had this issue for a while and don't know what's causing it. I rarely use the fogs. So, it's never been a priority to fix them. I've replaced the relay and fuse and still get the same result. I have yet to check the BCM. Any other ideas?
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Offline Sol Asylum

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Re: Simple reroute DRLs to Foglights mod (for HID users)
« Reply #11 on: December 17, 2013, 11:48:47 PM »
Check for a bad ground.
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