Foglights Auto On

Lamby66 · March 28, 2017

The fog light switch is in fact a momentary contact switch which pulls the BCM fog light control to ground. I will ponder this later but I think this should not be too hard but might need two more relays or a flip-flop

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Lamby66 · March 28, 2017

I think the big problem with this circuit (at least in my configuration) would be any toggle of the fog light switch would then tell the BCM the fog lights are on and disable the high beams. If I used a flip flop the fog lights would not always be in sync with the BCM and would cause issues with the high beams.

If the op explains better what he wants I can make this but ideally the fog light control would need to be removed from the BCM entirely (cut wire) and is NOT something I am willing to do

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gabbygenier · March 28, 2017

Hey Lamby

Sorry, been a busy week and didn't have time to investigate the fog light switch but looks like you've already figured it out.

What I'm looking for is for the fog lights to turn on when the lights come on, so the low beams, but also be able to turn them off if i want to. Essentially the simple diode would work but then i can't turn the fogs off if i want to

I'm not worried about the fog lights being on or off with the high beams so that part isn't a must if its too hard to do.

arcasey · March 28, 2017

Unless I'm mistaken, you can do the diode trick to have the fog lights on with high beams. The circuit that gets controlled with the fog light switch would need to break the fog light circuit down stream from the diode and the switch in order to have control of the fog lights and still maintain auto on.

Lamby, would it actually cause problems with the BCM if the fog lights are out of sync? The high beam switch should work no matter what state the fog lights are in because all it should control is the head lights. The BCM is only disabling the fog lights based on the Head light state (high or low beam). Then, if a user wants the fog lights to run with the high beams then all they need to do is the diode trick.

At least that's my line of thinking and I am by no means an expert.

Coby7 · March 28, 2017

What I'm looking for is for the fog lights to turn on when the lights come on, so the low beams, but also be able to turn them off if i want to. Essentially the simple diode would work but then i can't turn the fogs off if i want to

Why would you need to turn them off once they're on? I did the simple diodes to low beam and DRLs and I'm happy with that, never feel the need to turn them off. They still turn ''OFF'' with high beams though.

Edited March 28, 2017 by Coby7

gabbygenier · March 28, 2017

Why would you need to turn them off once they're on? I did the simple diodes to low beam and DRLs and I'm happy with that, never feel the need to turn them off. They still turn ''OFF'' with high beams though.

Why not is the question?

I'd like to have the fog light switch still work as it should from factory.

Just my preference.

Lamby66 · March 28, 2017

I started to work on a concept that would then use a latching relay that would be triggered by the foglight button to kill the fog lights. The problem with my circuit so far is that it does not reset until the power removed... it might work as long as the lights and bcm are in "sequence".. I will have to ponder more.

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Lamby66 · March 28, 2017

I will have to test this, but not on my truck as mine is already modified as I see best, but I think this will work for what you want... if you don't care about the fog lights with the high beams it gets MUCH easier

.

I will make a cleaner drawing in a little bit

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Lamby66 · March 28, 2017

Here is a drawing that makes more sense.

When you turn on your headlights, or auto headlights turn on, K1 will energize pulling the wiper to the normally open circuit tied to ground.

The output of K1 feeds the normally closed position of A side of K2 via a 1004 diode. (This normally closed location also is the point you tie the high beams is needed)

The wiper of K2 A feeds the foglight control relay (x5-pin 10) where a low would turn on the lights.

When you press the foglight button the first time you will then energize relay K2 connecting wiper B to the normally open circuit which is tied to ground. This completes a loop latching the relay to the energized position. Which will disconnect the A side wiper from the previously active K1... HOWEVER since X5 pin 10 is switched by BOTH the relay K2 AND the BCM, the low signal at X1 PIN 15 will make the BCM turn on the fog lights (and the dash icon which was off until this point).

Since K2 is latched it will not be de energized until the truck is turned off but is no longer needed. Each press of the fog light button after the first will then change the state of the fog lights via the BCM as designed by GM.

when the truck is restarted both relays are deenergized until they are needed again.

This "should" be exactly what you want.

Again I am not going to tie this into my BCM but it should work perfect based on the logic that I am already using for my circuit (just adds an interrupt circuit)

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Coby7 · March 28, 2017

Or maybe simpler just have a relay turn the fog lights on when either of them turn on and then disengage with an RC constant.

Lamby66 · March 28, 2017

Oops here is the picture.

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Lamby66 · March 28, 2017

Coby, the low beam is a logic high and needs to be inverted. I am not sure what the tank circuit does in your drawing.

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Lamby66 · March 28, 2017

Ohhhh I see what you did there. The tank circuits bleeds down the relay so the momentary contact can trigger the output of the relay. Very nice. Is there a logic low low beam pulse somewhere in the BCM inputs?

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Lamby66 · March 28, 2017

Coby, I forgot.. if you do it your way it will disable the auto dimming high beam function (if equiped) the high beams will not automatically turn on if the BCM senses the fog lights are on. That is why I went the way I did.

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