I found a workaround that will work with the OEM fog light switch and relay in the under hood fuse box. I found a negative trigger self latching relay module for under $10 where you can bypass the BCM and use your factory fog light switch and wiring.
So if you want to do this you will have to cut two wires out of the BCM plugs. The first one is the orange wire that runs from the fog lights switch it's located in the purple plug C3 pin B5 this wire is a negative momentary trigger that will hook to the left pin on the self latching module (see picture). The second wire is located in the Lt blue connector C2 pin A7 dark green with white stripe. This wire is a negative trigger that turns on the under hood fuse box relay for the fog light. The underhood relays only powered when the parking lights are headlights are on. A simple way to test is to unplug all connectors from BCM and use a regular test light ground one in and probe the dark green with white stripe in connector to C2 A7 . The little yellow light in the OEM box switch should light up showing that the relay is on.
On the self latching module connect DC+ to light blue connector C2 pin B6 Brown that is the parking light wire. Then connect DC - & COM two brown connector C1 pen A1 black wire (ground). Now connect N.O (normally open) to dark green with white stripes on the light blue connector C2 pin a7. The self latching module will simulate what the BCM would do if it was programmed. Nice thing about this module the fog lights will still work when you go to high beam. For pins A1 in connector C1 ground wire you can use a t-tap to connect and for pin B6 in C2 connector also use t-tap. This self latching module has very low current draw so t-tap will work fine or you can splice and solder that's up to you. The self latching module will be only powered if the parking lights or headlights when they are on so no parasitic draw when parking lights or headlights are off. Now for the under hood connection that is C4 connector headlight harness pin E2 is the fog light out. It is easy to add a wire to this connector just go to your local wrecking yard and pick one out of a connector or you can pick up a complete headlight harness with fog lights for about 10 to $15 at most you pull a part. Just make sure the fog light wires in the right location E2 some years may vary.

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Nice!!!

I've been working on a circuit to allow a full bypass of the daytime running lights (DRL) system. My Blazer was delivered to Canada so that the DRL system cannot be disabled.

I've not tested it yet but I was attacking it much like you have. I even used a latching relay system too. Although I like how your system is so simple. Mine is much more involved as you can see. I use relays to disconnect the DRL circuit from the external light switches. I added a push button switch to the standard headlight switch to toggle between the manual and DRL system. I'd be happy to share my circuit diagram if you like.

Does your disable the DRL system too so you could drive with only the parking lights and the fog lights if you want?

 

I found a easy way around the DRL just replace your high beams with LED and DRL no longer functions. But dusk to Dawn still works so the lights will come on after dark and shut off when the sun's up.

 

LEDs for the high-beams. Yes! That is a great work around.

I designed my circuit to also override the auto-headlights so I think I'm still stuck with the full circuit I made.

 

It was an accidental find. I replace my high beams and low beams with the LEDs then I noticed the DRL didn't work anymore so I did it to my 03 GMC Sonoma and it works on that also no more DRL. This is the LED kit I used

https://www.amazon.com/gp/product/B07JNV9TKM/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

https://www.amazon.com/gp/product/B07JNV9TKM/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

I'm thinking of adding fog lights in the future but I don't want to mess with the bcm so am just going to get a harness kit for fog lights and just run it independently but I want to use the factory fog light switch. I got a dash bezel from a Bravada online for the double din opening and it has the headlight/fog switch combo already installed so I kept it in for future use.

I know it's a momentary switch and will need a latching relay to make it work like a on/off rocker switch. So the harness kit I found comes with a rocker switch that uses 3 wires to connect it. Positive In, Positive Out (Relay control), and negative. Then I looked around and got the wire diagram for the factory momentary switch. I have found some latching relays but not sure if they are what I need but I can't wrap my head around how the two sides would connect to it (signs of being older I guess).

This guide if I'm correct still uses connection from the bcm correct? What would be the way to just straight wire a harness kit with POS in, POS out, neg to a latching relay, then to the factory switch. This is the latching relay I was looking at,
Thanks for the info and help!