2005 OBXT Ltd Obsidian Black 5MT
Fog Lights without Headlights
This modification was made on a 2005 OBXT Ltd. I assume it will work on all 05's and should be similar through MY2009.
NOTE: Use caution when working with the wires, especially wires located in the steering column. I accept no responsibility if you short out your wiring harness or injure yourself by setting off your airbags. You've been warned.
Disconnect your battery to be safe.
Tools needed: 10mm socket, Phillips screw driver, wire cutters, razor blade and wire strippers, soldering iron and solder, electrical tape and heat shrink tubing. Heat shrink is optional.
Overview: This modification will allow the use of the factory fog lights independent of the headlight function. The fog lights will be tied to the parking lights and still turn on and off with the stalk switch.
The first thing I want to get into is the operation of how the fog lights work normally.
If you look at the wiring diagram for the fog lights in the service manual, it looks deceptively simple.
In this diagram it shows the fog light relay coil positive signal comes from the daytime running light module and the coil connects to ground through the on/off switch in the turn signal stalk, and that's it.
But looking closer at headlight wiring section, you can see that is not the case.
If you follow the +12 path that I've marked from the DRL module you can see that it does indeed go to the positive side of the coil, but also see that it goes on to connect to the low/high beam selector. When you select either pass or high beam position, it connects the line to ground which is what causes the fog lights to shut off when high beams are on.
Secondly, the ground side of the coil does not go straight to ground from on/off switch in the stalk.
Following the red/white color wire line at the bottom marked with a "D" under the diode marked B85, you can see that it goes to the DRL module and also to the low/high beam selector and that it only connects the negative side of the relay coil to ground when the low beam headlights are on.
If you have performed the DRL disable by pulling the white connector from the DRL module, then that makes the red/white line disconnected from the DRL.
So now let's get into the nitty gritty of how I modified the wiring.
Remove the under dash cover, dash cover, knee protector and lower half of the steering wheel cover.
This is what the diagram will look like when we're done. Green lines denote new connections.
I started by tracing the red/white line that is shown going to the stalk in the steering wheel. This is the hardest wire to get to and the only place I found enough room to work with was to actually get at it under the steering wheel itself.
Here is the underside of the steering wheel with the plugs unplugged.
The plug on the far left, marked as B71 in the diagrams, contains the red/white wire that goes to the fog light relay and the black/white wire that runs to the parking light relay.
Here are the two wires we're looking for. The red/white and the black/white.
In the diagram you can see that I am cutting the red/white and soldering it to the black/white. Do not cut the black/white wire.
The remainder of the red/white wire is just left unconnected. I always cut my wires with a just enough so that if I need, I can reconnect at a later time. Just make sure to cover the bare end of the wire and then tape all the wires back up.
Moving on to the +12v side of the fog light relay, we focus on the relay bank attached to the right side of the fuse panel on the left side of the dash.
The two relays we are focused on are at the bottom. The relay on the left is the fog light and the right one is what is marked in the diagram as 'daytime running light relay.' The DRL relay is actually the path to ground for the headlights. So it is marked incorrectly as far as I'm concerned.
Detaching the relay block from the fuse panel is fairly easy with just two tabs then pulling it towards you and allows it to be turned over for easy access to the wires.
The wires we're looking for are a green/white wire going to the fog relay and a green/blue wire going to the DRL relay. The green/white wire is a slightly higher gauge wire, but this has no effect since we're running it elsewhere.
We're going to cut the green/white wire and solder the portion going to the fog relay to the green/blue wire running to the DRL relay.
The reason for this is because the positive line to the relay goes through the DRL box and it cuts off the power if the headlights aren't on. Doing this also bypasses the low/high beam selector, so that the power doesn't get interrupted when the high beams are on.
Tape up the bare end of the green/white wire that runs back into the dash as this will still be carrying +12v when we're done, but it's now useless to us.
Once you get all the wires properly taped/heatshrinked/protected, put it back together and marvel at the way the lights should look.
The foglights will now come on with the parking lights and are unaffected by the high beams. :29:
Feel free to post any questions or comments.