DIY: instead of DRL headlights, have your fogs (or anything) act as DRL
First, let me say I havent done this to my car. I'm writing it up for someone else. If it doesnt work or you think there is a better way, feel free to reply. As with any mod in your car, if you dont know what you're doing or I give you bad info, you're risking blowing up your own car its your risk.
There is a DRL fuse and relay in the cockpit fusebox. The BCM sends a ground signal to that relay, it clicks on, and provides voltage to the headlights (through a wire that runs through the bottom of the "underhood" fusebox), which is what your Daytime Running Lights are. If we use that ground to click on the fog light relay instead, we now have foglights as DRL and not the headlights. If you're more technically advanced, you can remove the "underhood" fusebox and cut and tap into the wire under the fusebox that provides 12v to the headlights during a DRL and use that 12v to trigger something. But an easier way that only deals with grounds is to run a ground from the BCM wire that signals the DRL relay to the "underhood" fusebox and shove that wire into the foglight relay so it clicks on instead. The hardest thing is running a small gauge wire from the BCM through the firewall to the "underhood" fusebox.
First, you need to drop the driver's knee panel to get to the BCM wires. If I remember its two screws by the ODB2 port and a few pop-out thingers. Once you can see the seven harnesses that plug into the BCM, you need harness X4 which is black. (X3 is blue and X5 is Brown, is that helps) DONT PULL ANY BCM HARNESSES WITH THE KEY IN THE CAR. KEY OUT. The manuals tell you to disconnect the battery for safety, but IMO thats overkill, its your car you do what you feel is safe for you. Unplug harness X4 so you can get to the wires better. You want wire #23 (look at the harness picture below), which is Purple and .3 mm2 (about 21guage) in size.
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As you can see in the pic its listed as "Headlight voltage" but that is in fact the ground for the DRL relay.
Now you have a choice: You can cut that wire so the ground signal no longer goes to the DRL fuse and relay, and attach (I recommend solder, but if you have to, use a vampire clip quick splice[shudder]) your long wire you're running to the underhood fusebox to the wire coming out of the harness, OR you can splice into the wire keeping the existing connection and merely tapping into it with your long wire. If you tap into it, REMOVE THE DRL FUSE AND/OR RELAY from the cockpit fusebox. This way you dont mess with the original connection and if you decide to go back to stock, you can just remove the new wire you ran through the firewall and plug your DRL fuse and relay back in and you're back to normal. But again, if you cut the wire you dont have to remove anything, but if you splice into it you need to remove at least the DRL fuse to disable the 12v coming from the other end of the wire. (cutting the wire or cutting the circuit by removing the DRL fuse=same thing)
Run your wire through the firewall into the engine compartment any way you please, and get it to the underhood fusebox. Find the fog relay, its in the top right corner of the fusebox (see pics).
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Pull the fog relay, and look on it for the diagram showing you which pin is #85. That is the pin the BCM gives ground to when you turn on the foglights in the car, and is what we're going to attach our wire to. Strip your wire a little more than normal, and push it into the hole for pin #85 and push the relay down on top of it. Make sure you got it deep enough to get squeezed in and connected but not so much exposed above the hole that it touches any of the other fog pins.
If this works for you, please reply so we know. I hate DRL and I leave mine off and I'm way too lazy to run a wire just to test it out.
Also, if you have Halo headlights or city lights or anything else you want to act as DRL, once you tap that wire at the BCM that wire can be used as a ground trigger to turn anything else on when the BCM is turning on DRL. You dont have to use it to trigger the fog relay.
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