DIY: Rear Fog Light Wire Via BCM and Stock Wiring

ChrisSlicks

If you disconnected the other end of the orange wire from the BCM and installed a fog light, yes. There is no fog light in our cars stock, just a place holder.

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spearfish25

Yep. That's the other option here if you've installed a real fog light. Tap an ignition switched 12v source into the orange wire with an on-off toggle switch of your liking. You'll be able to turn the fog light on at any time (even with headlights off), and it should turn off when you shut down the car.

As Chris said, I'd disconnect the orange wire from the BCM rather than just splice into it while still connected.

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spearfish25

Does the supply voltage go as high as the battery voltage in the center gauge cluster (14.4v)? When I use a multimeter, I always get right around 12v in various circuits. But as you said, I'd need a 610 ohm resistor for a 14.4V source and a 2.2V LED.

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ChrisSlicks

Reading the service manual it does explicitly state 12V so that should mean that the voltage is regulated. In other parts of the manual if a circuit receives full battery voltage it will indicate that. Sorry for the scare.

I usually under-volt LED's by 0.1 to 0.2V to extend their service life, but in this case I don't think it is going to matter whether the LED lasts 10,000 hours or 50,000 hours.

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spearfish25

I just got done installing the new switch. Thanks for the reassurance about the regulated voltage. The LED hasn't blown, so I assume you're right on .

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ChrisSlicks

Looks much nicer for sure. Perhaps a bit bright for my taste, but that's an easy fix when you choose your resistor.

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edconline

Ok question. I just replaced my factory rear fog, which has the momentary switch on the headlight stick and the indicator light on the dash already. I replaced the factor fog light with the evo r light. I assumed, I could just plug the new light in, in place of the old fog light using existing wiring and everything would work th same. However, when I wired it in, I found that the new light only illuminated for a quick flash when the switch was toggled then Went out again.

The old light only had two wires coming off it, red and black. I wired these into the positive and negative connections on the new light, but got the result described above. What am I doing wrong?

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ChrisSlicks

The EVO-R fog light has a flash circuit in it, I don't think that would be compatible. I think it is designed to be wired into the reverse lights or something like that.

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spearfish25

I've never seen the Evo-r. My guess is the stock harness you plugged into it is actually wired to the flasher circuit in the Evo-r and not the constant light circuit. You could try cutting off the factory harness connector and wiring the Evo-r connector to the end of the factory harness. Hopefully Evo-r packaged a wiring diagram so you'll know which circuit is the constant on.

If you wanted reverse flashing, you'd splice into the reverse lights and run the wires to the second circuit in the Evo-r.

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edconline

The evo-r has 3 wires. Ground, constant on positive and the flash wire. I tested it off of the normal accessory power an it works perfectly as advertised, there is also no need to hook up the flashing wire in order for it to work as a normal on/off light. This has something to do with the way the stock light is wired up, is there somewhere that shows what the black and red wires connected to the stock light are delivering?

Originally I had tried just cutting off the stock harness and wiring into that, double checked all the connections, same result with the quick blink on then off. Almost like the voltage wasn't staying at the plug, but the stock like works perfectly somehow..

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spearfish25

The stock wiring delivers a constant 12v. The black is ground. The red is your 12v power and should go to the constant source wire of the Evo-r. if you want reverse flashing, splice the intermittent wire from the light into a reverse light wire.

I'd use a multimeter to check the red power wire going to the stock light just to be sure if doing the above doesn't work as expected.

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edconline

I will use the multimeter and Double check it again tonight. However last night while doing the install, the red wire was definitely not giving a constant 12V to the evo-r fog

Side note, I tied the flashing into the brake lights so it will flash while braking. Also hid a switch in the cabin to disable the flashing function, probably only have it flash with brakes at the track or for 'aggressive' street driving. The constant on is temporarily tied into the parking lights.

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spearfish25

I'd be surprised if the 12V line in the factory harness isn't a constant 12V. I've wired my switch LED to the orange power wire coming from the BCM going to the rear fog, and the LED is always constantly illuminated when the fog is on (fog's power also powers the LED).

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ChrisSlicks

If there isn't enough current draw on the wire then it may turn itself off thinking there isn't anything connected (this is an LED fog light which probably draws considerably less power). Likewise if there was a short it would also shut off to protect itself. If it is the former then a high wattage, low value resistor could be added between the orange wire and ground somewhere near the fog light to suck up some extra current.

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spearfish25

Sounds like Digikey will be his friend. They have resistors out the whazoo.

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