Add the jumper underneath the fuse box then. All you’re doing is triggering both factory relays at once. There’s still fuses and relays for safety. I just want to make sure the wire doesn’t get hot but it seems fine.
What did you do to your NNBS GMT900 Tahoe/Yukon Today?
- Thread starter phattyford
- Start date
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Geoffsfas10
Full Access Member
eh...this is already done and wired in. Its good enough for me.
gooffeyguy
Tom
How did you wire the relay?Actually did Tahoe stuff this weekend.
Yesterday I did the air cabin filter retrofit, super simple and easy.
Today I wired in this relay
so now my fogs stay on when I turn on the high beams
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gooffeyguy
Tom
Doing it this way with the wire in the fuse box, do you still have control of the foglights with the switch, or do they just come on all the time ni matter what?
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Geoffsfas10
Full Access Member
The fogs are on anytime the headlights are on and vice versa. All it’s doing is jumping the fog light relay at the same time the headlight relay is triggered or vice versa. Both relays get triggered from the same signal. The fog switch is momentary, it doesn’t stay pushed in. It just sends a signal to the bcm, which turns on the relay. The headlights will come on if you push the fog button, in which case the fog indicator in the cluster comes on. But if you just turn the headlights on or if they come on automatically the indicator doesn’t come on when the fogs come on.
So I guess you could say you can control the fogs with the fog light switch but it will turn the headlights on too. But I can’t picture a scenario where I would want the fogs on without the headlights.
CaptainAmerica1
Full Access Member
AVS vent visors
One last note- the reason I noted the fog light switch is momentary is so you know that if you push in the fog switch and it turns the headlights on ( you don’t need to ever do this btw), when you turn the ignition off it goes back to all lights off when you start the engine again -unless the auto headlights turn everything on. The switch doesn’t stay “on”.
They’re wrong where they say the method I use piggybacks your fog lights on your high beam fuse. The headlights have a relay which is powered by a fuse. The fog lights have a relay which is powered by a fuse. The relays are triggered by a ground from the bcm. All I did was tie both ground triggers together so both relays come on with a signal from either output from the bcm. I don’t like it when someone states they have a “proper” way to do something but in reality don’t really understand the circuit they’re modifying. Now you have two fuses and two relays for your fogs. You only need one, the factory one. That just makes it over complicated. To me, that way isn’t proper. Or cleaner. What is clean is jumping both triggers from the bcm together. I’m gonna figure out which two wires those are and do it that way. Should be pretty easy.
gooffeyguy
Tom
So since the yukon uses the headlights as daytime running lights, doing this mod would have the foglights come in also during the daytime?
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gooffeyguy
Tom
When it's really foggy, I've turned my headlight knob to the momentary left position so it turns off headlights, then push the foglight button so just the parking and foglights are on.
With them being lower to the ground the light isn't reflected back into the drivers face as much and makea it easier to see while driving in fog
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There’s a separate DRL relay that’s triggered by a different wire from the BCM than the one that triggers the headlamp relay so that should be no. I’ll check tomorrow. If you look at the schematics you can see the negative signals from the BCM. The fog relay is D-GN/WH going to pin 86 on that relay, the headlight is PK/WH going to pin 85 on that relay and there’s another trigger that goes to the DRL relay. I’m jumping the fog and headlight trigger together.
Edit: now that I look at it, the fuses are after the relays so there’s no way to “piggyback” two lighting circuits onto one fuse. I checked and those fuses only show voltage when that set of lights are on.
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Then don’t do it the way I am.
gooffeyguy
Tom
Does it work? LolI do this.... not for fog but to look ‘cool’..... lmfao ......lol ..
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George B
¯\_(ツ)_/¯
I do too. I just wasn’t going to admit it first.I do this.... not for fog but to look ‘cool’..... lmfao ......lol ..
You could add a diode in the wire if you wanted to run fogs without the headlights on, that way when you turn the headlights on the fog relay would turn on but when you turn the fogs on the diode won’t allow the headlight relay to turn on. I’ll see if I can find a diode and try it today.
Nope.....lol
yes or it should anyway I haven't tried it yet I just looked to see if the relays were in the same position or not and they are. when the system switches at dusk to automatic headlights it cycles the relay (I can hear it) not sure what it would do at that point.
