Independent Fog Light Control by arpypat

By diyauto
( 2 )

8 minute read

Independent Fog Light Control

Compliments of arpypat @


This DIY is for independent fog lights (fog light control W/O headlights on)

First off, I'd like to thank everyone who laid the groundwork for this to happen. there are a lot of great people on this site who have sprinkled very useful information all over this forum. I made reference to the following threads while performing this DIY:


So I converted my halogen fog lights to HIDs, and while i was very happy with the output, I was always disappointed that they only work with the headlights on. I was able to run fog lights with parking lights on my RSX. In my Altima, I was able to control fog lights with the factory switch and parking lights by cutting a wire in the switch stalk and running it to the fog light relay under the hood. It is not this easy in the 4G TL, as the electrical system contains digital signals and MCUs.


An easy fix that does not compromise the car's electrical system is to install a new, isolated circuit. This is done by adding a switch, a relay and using new connectors for the fog lights.


The relay consists of a switch and an electromagnetic coil. The idea is that you can use a low current coil circuit to control a high power circuit. When current travels through the coil, it becomes energized and acts like a magnet. in doing so, the magnet closes a normally open contact in a switch. When the coil is de-energized, the magnet opens the switch contact. This switch inside the relay will close the circuit between your battery and your fog lights, and you will be energizing the relay coil via a switch in the cabin.

Here is an image of a single-pole, double-throw relay:

Pins 85 and 86 are the ends of the coil. Energizing the coil will close the contacts between pin 30 and 87 and open the contacts between pins 30 and 87a

Here is a generic wiring diagram using an SPDT relay to control fog lights:


- 35W Morimoto HID kit H11 (optional)

- Accord fog switch part# 08V31-SDN-1M035

- Accord fog harness part# 08V31-SDA-10030 (optional)

- (2) H11 female pigtail connectors

- 12 VDC SPDT Automotive Relay 30/40A (preferably with socket harness)

- In-line Fuse Holder w/20 amp fuse

- 18 gauge Power wire (at least 25ft roll to be safe)

- 18 gauge Ground wire (25ft)

- Crimp connector for 18 ga wire

- Wire ties

- Electrical Tape

- Digital Multimeter

If you want high-quality HIDs, the Morimoto ones from The Retrofit Source are the way to go. I bought everything else on Amazon.


1.    If you want to save yourself $20 and not buy the Honda switch harness, start by creating a wiring harness for the accord switch. There are 5 pins on this switch, 2 of which we are not going to use because it just for illumination of fog light symbol. The green light on top will still light up when the switch is on, so don’t worry.

Here is an image of the switch:

Pins 1, 2 and 5 will be used, so cut (3) 8”-12” lengths of wire with connectors and attach them to these pins.

If you are uncomfortable with this step, then I suggest buying the Honda switch harness.

2.  Pop the blank cover out near the VSA switch with a flat-head. I suggest fishing in the wires for your fog switch first and finding them under the steering wheel before popping the new switch in. Leave the wires hanging there for now.

3.  Create new harness for fogs: You will be wiring the new H11 pigtail connectors in parallel (connect positive to positive and negative to negative). Give yourself about 7-8’ between the two connectors and leave one end of the crimp connector open on the driver’s side. 

4.  Run wire through firewall. This is explained in one of the links above. Looking in the engine bay, there is an unused grommet in the firewall located slightly off-center towards the driver’s side and about 6” down. Get a long screwdriver and pry the grommet out. Stick the screwdriver in to poke a hole through the insulation. Now use a coat hanger (or similar) to fish a line through the firewall. You should find it inside the car near behind the accelerator pedal. 

5.  Connect this wire inside the car to pin #1 or #2 of the accord switch. 

6.  In the driver’s side fuse box, there is a 7.5A fuse in slot #17. Pull this fuse and install the Tap-a-fuse with another 7.5A fuse. Connect this wire to the other wire on the accord switch (pin #1 or #2 depending on step 5)

Note: Fuse #17 is a switched ACC slot, meaning that it is only powered if the car is in ACC mode or if the car is running.

7.  Connect the wire on pin #5 to chassis. You can verify ground by taking your multimeter and set it to check constant (DC) power. With the car in ACC or on, check the voltage between the fuse #17 and any nut/bolt which you see connected to chassis. You should be reading >12 VDC. Connect the ground wire to this nut/bolt.

8.  Everything in the cabin is now complete. I suggest testing the switch. With the car on or in ACC mode, check the voltage of the wire hanging through the firewall. When you hit the switch, this wire should be reading >12 VDC and the switch should light up green. If the switch works, turn the switch and car off.

9.  Install the relay. I screwed the relay into the bracket holding the lower half of the factory air intake box. Connect the wire going through the fire wall to pin 85 on the relay harness. Do not yet connect the relay harness to the relay. 

10.  Now you want to connect the new fog light harness to your fog lights or HID transformer. There is a DIY in a link above that shows how to access the fog lightsand how to install HID fogs.

You want to remove the factory connectors and tape them up. Connect the new harness to your fog lights / HID transformer. Run 2 wires down near the battery to the fog light harness and connect one to positive and one to negative of the harness. The other end of the positive wire will connect to pin 87 of the relay harness (normally open contact). The other end of the negative wire will connect to pin 86 of the relay harness.

11.  Connect relay harness to ground. I used a common ground for the fog lights and the relay. Take a wire from pin 86 of the relay harness and connect it to chassis. Use the same method of finding a valid ground point as in step 7. I used the bolt holding the bracket for the intake box neat the hood strut. Sand down the black paint and connect the wire to this bolt. 

12.  Connect the inline fuse to pin 30 of the relay harness. You want to make sure you have a 20 amp fuse as well. Connect the other end of the inline fuse directly to the positive terminal of the battery.

13. Finally, connect the relay harness to the relay. You are done! If you did everything correctly, you should now have control of your fog lights with the new switch. Turn your car on and try it out!

This whole procedure took me about 3 hours. Took almost as long to write this DIY! Goodluck


Edit: Forgot to mention a required part - Low profile Tap-a-fuse

Thanks! Its not an original idea, but it works:

Slightly off color but not too noticeable in low lighting

And I doubt there is a switch stalk that will work.. I think base models come with foglights too?