Acura MDX SUV Forums banner

Rewiring Fogs

30512 Views 80 Replies 35 Participants Last post by  midnightMDX
I have not had the chance to try this. On the TL website they are doing it to their '02 TL's. I must warn you this is a lengthy, but very imformative post.

How to wire fog lights to come on with just the parking lights.
Okay, for anyone that wants to run their fog lights with just their parking lights on, I've figured out how to do it. I did it on my '02 TL-S and it works fine. I know some posted here before wanting to know *why* someone would want to do that (I believe in some states like CA it's illegal to run just fogs), but here in MA you can run just fogs and parking lights at dusk, in the rain, etc. Or if the fog is so thick that just fogs gives you better visibility you can run the fog/parking combo without low beams (even at night). This post may seem lengthy but I tried to be as explicit as possible. Maybe this can get added to the FAQ.
First my warning: Although is mod is 100% effective and safe to do, I absolve myself of all claims of damage to your vehicle should you not be able to complete this mod correctly (or you pound a couple 40s before trying it).

Time to complete: 20-30 minutes, even for a beginner
Tools needed: Short phillips-head screwdriver, small pair of scissors (or razor knife), some type of in-line electrical connector, crimping pliers for electrical connector

Background: Because laws vary from state to state, Acura must make sure that its lighting is 50-state compliant. So even though some states allow it, they must wire the car so the fog lights (a) cannot be operated independant of the lights, (b) cannot be operated with just the parking lights, and (c) cannot be operated when the high beams are on. This mod changes the fogs so they will now do (b) in addition to how they normally function.

What the mod does: When the fog light switch is pressed, the current wiring system has the first fog light relay (there are two--this one is in the passenger side footwell) check the position of the light stalk. If it is switched off or to parking lights, no power passes to the second relay which powers the fog lights. Once it is switched to low beams, power passes through the first relay which then in turn powers the underhood relay and sends the high voltage (20A) to the fogs and lights them. The mod rewires and fools the fog light switch into thinking the low beams are on when the light switch is moved to the parking light position.

1. Remove cover from driver's side fuse panel. This cover is the entire end-piece of the dash. You need to open the driver's door fully to properly access this panel. It is held in place only by pressure clips. Simply pull up and out at the very bottom to start the loosening process. Gently apply pressure to the side closest to the driver and the top and the whole cover will pop out. Notice there is a long ridge on the side closest to the firewall. Make sure that side goes in first when putting the cover back on.

2. Loosen left side of driver's underdash kick panel. Although you could remove this whole piece, you only have to loosen the left side near the fog light switch to do this mod. Looking in though the opening you just made with the cover removal, you should see two brass-looking phillips-head screws. One is close to the front of the dash, one is down behind some wires holding a long thin brace in place, closer to the firewall. This is the screw you need to remove. It is the *only* screw that holds the driver's side underdash kick panel in place. Once you've removed the screw, you can loosen the left portion of the underdash kick panel by gently pulling on the piece. There are two clips at the top front, close to the bottom of the gauge cluster. You pop these clips out and the left side will come away from the dash. *This is as far as you need to remove the underdash kick panel.*

3. Unplug wiring harness to dash light dimmer switch. This is a simple plug harness that is indexed so it only goes back one way--no need to remember how it went in. This gets the cables more free for the next step.

4. Remove the fog light switch from the dash. Easiest way is to reach in from the side and grab it gently from behind (sounds like some of my dates). Squeeze gently top and bottom and push forward (towards where driver sits). The switch should pop out and be hanging by its wiring harness. Unplug the wiring harness. Press the tab in on one side of the harness and pull gently out. Set the switch aside and push the wiring harness back through the opening and bring it out through the side so you can work on it easier.

5. Spice the wires. The wiring harness consists of an inline, 5-prong plug, which is connected by five 18-20 gauge wires that are individually exposed for about an inch and then are bunched together by some rubber conduit tubing. Take the scissors or razor knife and carefully cut open the tube to expose more of the wires. You need to cut back about two inches, because you're going to want about three inches of slack to work with. Once you've cut the tubing, fan all the wires flat. You have five wires going to the harness. They are:

1. White/Blue - Ground side of indicator light (green light that shows fogs are on)
2. Blue/Red - Power to passenger side footwell relay
3. White/Red - Power from headlight switch
4. Red/Black - Power from taillight relay
5. Red - Connection to dash light brightness controller

Wire number 4 provides power to the icon on the switch whenever the lights are on (parking lights/taillights are all on one circuit). Wire number 3 provides power through the fog switch *only* if it detects the headlight switch in the low-beam position. So what we do is splice wires 3 and 4 together, thereby bypassing the headlight switch altogether. Now, whenever the taillights have power, so will this leg of the switch and the fogs will come on when the switch is pressed.

You can use whatever means you wish to join wires 3 and 4 together. Just remember you *don't* want to cut them, just splice the two together. I highly recommend an inline automotive wiring splicer (the kind that looks like a double-barrel shotgun from the end). These types of splicers are meant to be slid on over an exisiting attached wire and a second wire's free end is slid into the other side of the connector. The connector is then crimped and the latch cover is closed. However, because both of these wires are connected at both ends, if you use this type of connector you will need to drill out or punch out the solid end of the connector so both sides are completely open on each end. Then simply slide the wires into the connector, crimp the metal blade down through the wires and snap the plastic retaining tab closed. If you're good with solder you can solder in a jumper between wires 3 and 4, but that makes the mod much more permanent. I strongly recommend a two-wire inline connector and crimp.

6. Reassemble the fog light switch. Take the wiring harness from the side and push it back through the hole in the dash where the switch goes. The wiring harness for the dash light dimmer control is sort of tied with this one so you have to make sure you keep them separate and only push the fog light harness through the hole. Snap the wiring harness onto the fog light switch (it can only go one way). Then gently push the fog light switch back into the dash opening (make sure it is right-side up--green light on top, icon on bottom).

7. Replug the wiring harness into the dash light dimmer switch. Self explanatory.

8. Reattach underdash kick panel by pushing gently in area of the clips until they snap into place (remember there are two at the top, just under the gauge cluster)

9. Replace the phillips screw in the brace for the dash panel.

10. Replace driver's side fuse panel cover. Remember to start it by inserting the side closest to the firewall first. It just snaps into place.

That's it--you're done. The only thing you've changed is now the fogs will come on whenever you have the light switch either in the parking light position or in the low beam position. NOTE: The fogs will *still* go off when you use high-beams so this mod will not cause trouble for those who live in a place where it is illegal to drive with high beams and fogs together. Making them come on *with* the high beams is a much more in-depth mod and will not be dealt with here. What's more, if your fogs are on and you shut off just the headlight switch, the fogs go off too (like the factory set-up). Remember it this way--whenever the taillights are on, the fogs can also be on (*except* for when high-beams are also on).

Whew! I know it seems like it is complicated, but this is a very easy mod. If you've crimped wires before in a car it's even easier. Most of you could do this in 20 minutes, no more than 30 minutes for a real beginner.
See less See more
1 - 9 of 81 Posts

It seems like the logical decision would be to splice the Red/Green and Red/Black wires together. I followed the original instructions by O-TownMDX for my 2002 MDX and they worked fine. Go for it and see if it works. Since you are only using an inline splicer, there would not be any irreversible damage if it does not work. If all goes wrong, I shall alert the bomb squad and your next of kin. Good luck.:)

Hmmmm. Something to think about. Neverthless, splicing the White/Red and Red/Black wires together on my 2002 MDX worked for me without any adverse effects. This mod. allowed me to run my foglights with my parking lights. YMMV.

"Nothing ventured, nothing gained." That being said, I shall notify the bomb squad to stand down.;)

Your point has been so noted. I sense your motivation is to be the voice of conservatism. The fact is many MDX owners, myself included, have performed this simple "no-cost" mod. with no adverse results. I love to be able to drive with the parking lights and foglights. So, for you brave souls willing to "throw caution to the wind", I say "step up to the plate and go for it.":29:

Your are welcome...glad to have your views in the discussions.:)
Re: Everyone relax

N_Jay said:
The relay takes fractions of an amp.
Even 24 guage wire will carry well over 1 amp.

To make everyone happy, pick up the same circuit, just get it off a lead running to a larger load, and therefore running in a thicker wire.
The same color code is typically the same circuit. (But test to be sure)
Sounds good to me.:D
Re: Re: Everyone relax

HrdTsk said:


What exactly do you mean with regard to the mod?

Do you have access to the 2003 schematics? Does anyone?

Sorry, with my level of expertise, I need the cookbook approach.
Come on guys. It looks like HrdTsk might be back in on the rewiring foglights mod. Let's talk some plain english and K.I.S.S.:1zhelp:


Q: If it takes a hen and a half, a day and a half, to lay an egg and a long does a roster have to sit on a doorknob to hatch a hardware store?:confused: :confused: :confused:
And they lived happily ever after.:)
  • Like
Reactions: 1
1 - 9 of 81 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.