Fog light - BCM - relay control?
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5th Wheeling
Joined: Feb 2024
Posts: 40
Likes: 11
From: Texas Hill Country
Fog light - BCM - relay control?
2019 F250 Lariat
It is my understanding that the fog lights are controlled via the dash switch through the BCM. I would like to use the supply wiring that feeds one fog light to switch a relay instead.
Will the BCM see this change and throw a code? I don't know if they are monitored for current (for example if one is out) and would see the current/ resistance load change.
It is my understanding that the fog lights are controlled via the dash switch through the BCM. I would like to use the supply wiring that feeds one fog light to switch a relay instead.
Will the BCM see this change and throw a code? I don't know if they are monitored for current (for example if one is out) and would see the current/ resistance load change.
Fleet Mechanic
Joined: Oct 2022
Posts: 1,822
Likes: 898
From: Dallas Metroplex
I did something similar, but using one of my low beam headlight wires to trigger a relay. In my case there was a low priority code thrown and stored, but doesn't trigger a CEL or fault. Headlight still works nominally, but the slight drop in current was obviously detected that triggered the code.
So, I think it probably wouldn't be any different for the fog lights, as the headlights and fogs are both controlled over the CAN Bus. In my case the relay functioned as intended, and I only see the caught code whenever I'm using ForScan, and just ignore it.
I probably should perform due diligence and install a diode on the trigger wire, so that any possible feedback voltage from my trigger wire doesn't affect the headlight circuit. It's on my to-do list...
So, I think it probably wouldn't be any different for the fog lights, as the headlights and fogs are both controlled over the CAN Bus. In my case the relay functioned as intended, and I only see the caught code whenever I'm using ForScan, and just ignore it.
I probably should perform due diligence and install a diode on the trigger wire, so that any possible feedback voltage from my trigger wire doesn't affect the headlight circuit. It's on my to-do list...
Thread Starter
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5th Wheeling
Joined: Feb 2024
Posts: 40
Likes: 11
From: Texas Hill Country
I did something similar, but using one of my low beam headlight wires to trigger a relay. In my case there was a low priority code thrown and stored, but doesn't trigger a CEL or fault. Headlight still works nominally, but the slight drop in current was obviously detected that triggered the code.
So, I think it probably wouldn't be any different for the fog lights, as the headlights and fogs are both controlled over the CAN Bus. In my case the relay functioned as intended, and I only see the caught code whenever I'm using ForScan, and just ignore it.
I probably should perform due diligence and install a diode on the trigger wire, so that any possible feedback voltage from my trigger wire doesn't affect the headlight circuit. It's on my to-do list...
So, I think it probably wouldn't be any different for the fog lights, as the headlights and fogs are both controlled over the CAN Bus. In my case the relay functioned as intended, and I only see the caught code whenever I'm using ForScan, and just ignore it.
I probably should perform due diligence and install a diode on the trigger wire, so that any possible feedback voltage from my trigger wire doesn't affect the headlight circuit. It's on my to-do list...
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