Lamby66

I did not do the replacement as it was under warranty. They removed the upper part of the fuse box on the drivers side. There is some circuity in the fuse block and the relay that is pictured in the schematic is actually solid state and not user serviceable. It is inside the fuse block. good news it its not super expensive to replace

Madcow, this is not for me. I was helping others modify the lighting control circuits. My mods work perfectly. My next mod will be a timer circuit added to my cargo light mod. Sent from my SM-N950U using Tapatalk

His fee is 200 for what would cost about $12 in parts and about an hour of time. Sent from my SM-N950U using Tapatalk

This is why I built the circuit I did. Launching duck boats at the butt crack of early and driving in campsites. My foglights turn off if the headlights are not on. The circuit I made for if you changed to X4-23 would work pretty sweet too. Foglights always on unless I turn them off. Sent from my SM-N950U using Tapatalk

I think X4-7 is data looking at the circuit. I think it controls the light control module. I dont think that will work for you. You can check X4-23 out of park a d this should go logic low (it disables the adjustable pedals when you are driving) X5-22 with X4-23 and you should then have fog lights when ever the truck is not in park.. the isolation relay still would work the same. Sent from my SM-N950U using Tapatalk

I understand. Did you check with the truck actually in drive? I think the DRL and parking light logic is the same. But you need to be in drive. I will have to see what the circuit you stated does but if it's a logic low when the drl circuit is on, it will work. I think the lights circuit is a little complex though. There is a data line that goes between the bcm and the lights. I think the DRL circuit is data and not logic. There is a transmission is not in neutral pin too.. also might be an option for you. Again it it's a logic low. If it is, just use that instead of the X5-22 pin. Sent from my SM-N950U using Tapatalk

We are close. The automatic foglights are tied to the running lights. They are on when the truck is driving or the lights are on. Pressing the fog light control might actually do two things the first time you press it. 1) it will energize and latch the relay removing the foglight always on mod. 2) it will probably tell the BCM to turn ON the fog lights and your dash symbol will light. Pressing it again will turn off the lights and then every additional press will turn them on or off. When you turn of the truck it resets the relay. It will then allow the DRL mod to work again until next time the foglight button is pressed. Make sense? Sent from my SM-N950U using Tapatalk

Here is a circuit that SHOULD work for what you need. Verify that the x3-5 pin is 12v on ignition which it looks like it should be. You will need a 12v 5a dpdt relay. They sell them on Amazon for like 8 bucks with the base (you can use it if you want or solder to the relay contacts) Make sure you connect a diode across the coil of the relay to prevent ringing. The cathode (bar side) needs to be on the ignition side of the coil. Operation: Then the truck is driving day ot night, the parking lights are on (drl) this is on x5-22 When the truck is started the relay is de-energized and the normally closed contact bridges the drl to the X5-10 FOGLIGHT control (protected by the diode in x5-22 The fog lights will be on if the truck is driving, or the lights are on. If you press the factory fog light switch (logic low at X1-15), the relay will close and stay latched due the normally opened contact on the 2nd circuit pulling the wiper to ground. This will isolate the diode between X5-22 and X5-10. The relay will stay latched as long as there is power to the relay via X3-5 (verify that is a good ignition power source) The fog lights will now function as factory fog lights. Not allowable to be in high beam and turned on and off by the switch. When the ignition is reset, so is the relay. The truck will go back to auto foglight mode. I take no responsibility for any actions that arise from you modifying your truck including blowing your BCM. DO THESE MODS AT YOUR OWN RISK!!! Sent from my SM-N950U using Tapatalk

Oops, I said that wrong... the high beam circuit is fine. It's the low beam circuit that is a 12v control voltage.. that is the one needs the inverter!!! Sent from my SM-N950U using Tapatalk

I can get you a circuit that works if your soldering and wiring skills are decent. I will post it when I figure out the BCM point for the fog lamp switch. Once you press the fog light switch, the foglights will turn off then can be turned back on via the switch. The automatic on circuit will not reset until the power is killed. Is that okay? DO NOT DIODE THE LOW BEAM CIRCUIT!!! that is a control HIGH output circuit. The logic low control circuits are not designed to accept voltage!!!! My schematic (posted earlier) used a relay as a logic inverter to make the high beams generate a logic low so I can use for the fog lamp control. Sent from my SM-N950U using Tapatalk

I can set you up with a circuit that can do that. The relay can auto latch and then the logic of the switch would release it. That is the way my circuit works. The only thing different with my circuit is I do not want my fog lights on during the day. No point in my eyes. Sent from my SM-N950U using Tapatalk

Yoderrm, do you have the auto dimming headlight option? If you do not, the circuit is much easier. You just need too take the ignition feed and reverse the polarity with a relay (like I did) then diode protect that to the fog lights circuit. Then your fog lights would be on whenever the truck is running. Which I think is what you wanted. The problem is if you auto dimming headlights, they can not know the foglights are on or they wont go to high beam on their own I dont have the circuit numbers here but if you give me a day, I should be able to look it up at work tomorrow Sent from my SM-N950U using Tapatalk

Thank you STKR, but I looked all over and tried to even use a "fox and hound" but I cant find that J302 that I need to access. I think my next best bet would be to go to the dealer and see if the service writers might have a clue. They sure pack stuff tight in these modern trucks ;-)

Yea, I think maybe my fox and hound toner might be able to help with this. There might be quite a bit that tones though considering this circuit goes EVERYWHERE ;-) Thanks again for your help guys Sent from my SM-G930V using Tapatalk

Pgamboa, I understand the circuit. I wired my cargo circuit to back feed from the trailer backup light circuit and a timer based button in the bed. I installed a diode to prevent the cargo circuit I designed from feeding the center high and mirrors. In an ideal design, I would like to include the center high light in my cargo light circuit but keep the mirror leds from coming on. A passenger compartment mounted double pole single throw switch would work prefect IF I can find where J302 is located. I was hoping there was a gm tech on here that would have access to the harness routing drawing to tell me where J302 is located. Per the upfitter guide, this is where the center high cargo light is tied to the towing cargo light circuit. Sent from my SM-G930V using Tapatalk

Ravenkeeper, thanks for the info, but tow mirrow lights are not puddle lights but blinding backup lights. I want to keep these off most times. I need to isolate them from the factory cargo lamp circuit. Sent from my SM-G930V using Tapatalk

Has anyone doing this mod, or a version of it, find the location where the towing mirror cargo leds are tied into the rest of the cargo light circuit? The upfitters guide says J302 under the left instrument cluster... That is not really too helpful as there is a mile of bundled wire under there.... I REALLY want to switch the use of these leds with a SPDT so they are Normal/Off/Reverse. I have a more complex but more useful control of my cargo lights operated by my backup lights and a latching timer circuit but that is only for my bed cargo lamps, as I cant find where I can turn off those annoying mirror LEDS separate from the high mount cargo light (which I would also like on with my circuit) Anyone able to help?

I soldered my circuit to small brad nails so I could make contact with the bcm connectors. Sent from my SM-G930V using Tapatalk

My wipers failed working, and I was able to get them repaired via warranty. Just as another member on this this forum, the repair required the replacement of the fuse panel of my truck (2016 sierra SLT with the 6.2 and max tow). The upfitters manual shows the washer circuit in perfect detail and has two relays (motor and speed).. I figured the relay failed, no biggie. The problem is that the relay is not a plug in relay in the fuse panel like you would expect. I think this is a TERRIBLE design on GMs part Has anyone replaced their fuse panel on their own outside of warranty and then able to actually keep their damaged fuse panel? I would like to know where these relays are in this panel and if they are repairable. (I am an electronics technician and can work on soldered on components if that is what this is) I think these are solid state opto-isolators (which can be TINY!!) If anyone has pictures of the tore apart fuse panel that would be great in case this happens again out of warranty. Thank you all in advance

Well Gabby, Did you get your fog lights working the way you want? Sent from my SM-G930V using Tapatalk

No you are not a pain in the ass, you want what you want. We all have our reasons. I am not sure what point on the BCM that Colby is taking the logic low for the low beams, but if there is a momentary logic low his design will work. If there is not a momentary logic low (which I did not think there was or I would have used it) you would need to do my circuit. Sent from my SM-G930V using Tapatalk

Colby without the auto dimming headlights, do you even need the relay or the rc circuit? Can't you just add a diode between your low beam control (not sure where that is on the BCM inputs though) and the fog lamp control? The two inputs in parallel would allow an either or logic state as well Sent from my SM-G930V using Tapatalk

Colby I am not sure what he has. I know I have it and wired it accordingly. I do like your pull down circuit design though. Were are working on the same goal :-) Sent from my SM-G930V using Tapatalk

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. Sent from my SM-G930V using Tapatalk

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? Sent from my SM-G930V using Tapatalk