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How to: Wire fog lights to come on independantly

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    • Jul 25, 2007 3:04:14 pm
    Introduction: Previous posts have only given instructions on how to make the fog lights come on with the parking lights (see this thread). Some people have mentioned that they were able to make them come on whenever the key is in the ignition, but none have posted instructions. Therefore, this post explains in detail how to wire the fog lights so that they can be turned on/off whenever the key is in the ignition in the "ON" position.

    Technical concept (for those who are interested): This is a simplified wiring diagram of the fog lights:

    As you can see, there is a relay that controls whether or not the fog lights can turn on. If the headlight switch is closed (headlights are on), then a current goes through the #3 and #4 prongs of the relay, causing the switch between prongs #1 and #2 to close, allowing for the fog light circuit to be completed and the fog lights to turn on. When the headlights are off, the relay keeps the fog light circuit open, so the fog lights cannot be turned on.

    So what we need to do is replace the signal from the headlight with another source that is on when the car is on, and off when the car is off. One such source is the ignition (on when the key is turned to "ON", and off when you pull out the key). This means that whenever the key is in, there is a signal being sent to the fog relay allowing the fogs to be turned on/off independently with the fog light switch. And when the key is pulled out, there is no signal to the fog relay, so the fogs cannot turn on (this is good because you can leave the fog light switch in the "ON" position, and the fogs will turn off with the car and you won't have to worry about draining your battery).

    Before you start: This post is intended for people who already have fog lights installed. If you are installing new fog lights, refer to the original post (How to install fog lights) for instructions. Then follow these instructions after the fog lights are installed and functioning.

    Time: ~15 minutes (assuming your fog lights are already installed)

    Flat head screwdriver
    10mm hex socket
    Wire cutter
    Wire stripper
    Electrical tape
    Piggyback fuse (optional)

    1. Disconnect the battery using a 10mm socket.

    2. While you are under the hood, take the fuse puller out from the fuse box next to the battery (open the fuse box by unclipping the two clips in front, then remove the cover. The fuse puller is the white thing clipped onto the inside of the cover of the fuse box).

    3. Press on the brakes a couple times to drain any power out of the system.

    4. Open the fuse box below the steering column.

    5. Locate the fog relay and pull it out. (If you don't know where the fog relay is, look in this thread.)

    6. Locate the gray wire coming out of the fog relay (Note: these instructions are written for OEM fogs and VRD fogs! If you have other aftermarket fog lights, the wire color may be different - check before you do any cutting!).

    7. Cut the gray wire, leaving enough length on the relay side to reach the fuse panel on the bottom (around 8 inches).

    8. Remove the plastic cover from the fuse panel on the bottom (you'll probably have to stick your head underneath to see the fuse panel).

    9. Using the diagram on the fuse panel cover, locate the IG2 fuse (fuse #30, blue, 15Amps).

    10. Pull out the IG2 fuse with the fuse puller.

    11. Strip the end of the gray wire coming out of the relay with the wire stripper, and bend the end of the wire into a hook or L-shape.

    12. There are several ways to tap the wire into the fuse, I used the first one (12a), but you can use whichever one you feel works the best:

    12a. Slide the L-shaped wire into the edge of the IG2 fuse socket. Try to fit the wire into the little slot on one side of the socket.

    (alternative) 12b. If you are having a hard time with the above method, you can try to wrap the end of the gray wire around one of the prongs of the IG2 fuse, and then push the fuse back into the socket to secure the wire there. (However, since the wire is pretty thick, the fuse might not push all the way in when using this method.)

    (alternative) 12c. If you have a piggyback fuse such as the one pictured below, you can use that instead to connect the gray wire (this is probably the safest, most realiable method). You'll need to connect a female spade connector to the gray wire to use this type of piggyback fuse.

    13. Push the IG2 fuse back into its socket to secure the wire. Try to push the fuse in as much as possible, you don't want the fuse to be falling out while you're driving. Also make sure that the wire is not touching both of the prongs of the fuse, or touching the prongs of another fuse. If you aren't sure, pull the fuse back out and try again.

    14. Put the fuse panel cover back on (if it fits over the wire).

    15. Tape up the other end of the gray wire with electrical tape and put the fog relay back in place.

    16. Reconnect the battery, turn the ignition to "ON" and test the fog lights (they should now be able to turn on/off independently of the headlights and parking lights).

    17. If everything works, then you're done. If not, check all the connections, fuse and relay, then try again.

    Disclaimer: Please follow these instructions at your own risk. Understand that there is the risk of shorting a circuit, blowing a fuse, or even starting an electrical fire if the wires are not properly connected. I will not be responsible for any injuries or damages to property resulting from this modification.

    BTW, I don't have any posts on these forums because I don't actually own a Scion. The car we did the mod on was my gf's car. I've gotten a lot of useful information from these boards to help her mod the car, so I thought I'd contribute something in return.
    • Jul 25, 2007 3:12:36 pm
    great write up bro im looking to do this in the future
    • Jul 25, 2007 3:16:10 pm
    Here are photos of the result:

    Full album here: http://www.acurainspired....m.php?aid=2054&uuid=5
    • Jul 25, 2007 3:17:42 pm
    looks that your tc
    • Jul 26, 2007 7:22:49 am
    slickshot wrote:
    looks that your tc

    Thanks, it's my gf's car actually. I just helped her install the fogs this past weekend. My car's the one in the back
    • Jul 26, 2007 7:38:21 am
    Very nice. Sticky time
    • Jan 05, 2008 9:31:29 pm

    worked like a charm for me =)
    • May 14, 2008 10:20:01 am
    thats a nice set up
    • May 14, 2008 11:09:28 am
    does this void your warranty?? i was told it does, dats why i haven't done that yet plus the "how to do it part " too!!
    • May 14, 2008 11:12:08 am
    ^^It will only void your warranty on the electrical systems if you start having electrical issues after doing this due to a botched install.
    • May 14, 2008 11:17:13 am
    ooh ok thanks!!
    • Jul 13, 2009 5:13:01 pm
    i just did the fuse thing on Saturday because before I did a crazy wiring that interfered with my high beams not working at all lol great write up!
    • Jul 13, 2009 7:31:26 pm
    Would this work if i wanted to add a toggle switch? Like to turn them on and off using the switch instead. Or would i just have to wire it to a power source and the switch?
    • Dec 27, 2009 8:59:29 pm
    DUDE worked perfectly! thanks so much
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