Damn it GM... (Fog lights on a 2018 Tahoe)

[littleblazer]

So as some of you may know and some of you may not, my mom treated herself to a 2018 Tahoe. Long story short the only damn thing she wants that it doesn't have is fog lights. Now much like our trucks, there is BCM reprograming required and the switch has to be replaced. But the problem is, the wiring is only present from the switch to the BCM. No wiring leaves the BCM to the under hood fuse block and no wiring leaves the fuse block to the headlamp harness... Even worse is if I add all the wiring, the fuse block has a different lay out (it would seem) for fog light equipped vehicles. Being honest, this just seems excessive but whatever. Funny side story, all the wiring is there on the Sierra, actually the plug is laying right behind the knock out. It just seems like a waste of money to have several different harnesses for the same truck.

Ranting aside, I have an idea to get around GM's crappy engineering. I buy just the fog lamp assemblies, since at least the front bumper is the same for equipped vs non equipped vehicles. Then install them. Then what I do is use a weather pack splitter on the headlamp socket and use the second feed as a relay trigger to run the lights hardwired from the battery like when doing a retrofit for projectors. It is the simplest and cleanest I could come up with since the headlights are only on at night and chances are she'll be using the fog lights all the time anyway. As an added measure, I could install the correct fog lamp switch and build a latching system to turn them off from the momentary ground pulse as well... My only real concern is the voltage sense with all the electronics and if the truck has a load that it isn't expecting, will things freak out... I really doubt it but it is a thought that crossed my mind. Any opinions and input are appreciated.

 

[Blckshdw]

I like the simple idea of triggering a relay with a split signal from the headlights. I know a few people who also use their fog lights all the time at night, whether there's rain/fog or not as well.

I wouldn't think the electrical load of an extra pair of halogen bulbs would be enough to cause problems. If you were trying to power an amp, or maybe an inverter, or something a little more thirsty... Might be a different story.

 

[Sparky]

Why not just wire them to a separate fog switch? No risk of any sort of weirdness that way.

Does the 2018 have a "bulb out" detection for the headlights? If not, then there should be no problem using the headlight as a feed to trigger a relay. If it does, it might affect the function of that feature, but not sure.

 

[littleblazer]

I think it's a resistance sensor and the resistance of a coil would be lower than what it's looking for. Idk if it has it but I know that the 03 did. That was also able to say front or rear on directionals...

As for the separate fog switch, my concern is more about total load sensed vs just worrying about an extra .1 amp on the headlamp. I don't see it being an issue but just a thought that crossed my mind. This is the newest vehicle I've touched so I'd rather not start hacking up things if I don't have to. This keeps it under the hood and would take all of 30 seconds to remove if I had to go back to stock.

 

[wstuckey1]

What about a set of pencil beam led pods? Or if you wanted oem look you could retrofit them into the fog light lenses. In my experience I've never had a set of fog lights that did anything but look good. They always seem to be aimed too far down to really illuminate anything

 

[littleblazer]

What about a set of pencil beam led pods? Or if you wanted oem look you could retrofit them into the fog light lenses. In my experience I've never had a set of fog lights that did anything but look good. They always seem to be aimed too far down to really illuminate anything

It is the sole reason I'm doing it. Too much black trim on the front without it imo. (The ones on the 03 can be aimed actually... those alone are better than the factory headlights on the trailblazer...)

 

[wstuckey1]

It is the sole reason I'm doing it. Too much black trim on the front without it imo. (The ones on the 03 can be aimed actually... those alone are better than the factory headlights on the trailblazer...)

I see. The ones on my tb are pretty much useless even after aiming them all the way up but they look cool when they’re on. And imo they look a lot better that the non fog light bumpers.

 

[mrrsm]

A Possible Inexpensive Solution?

http://rover.ebay.com/rover/1/711-5...0001&campid=5338077216&icep_item=292639680154

 

[Sparky]

No. Just no. Those aren't fog lights. They don't have proper beam patterns. I want to strangle everyone who uses light bars on the roadways with other traffic around.

 

[wstuckey1]

No. Just no. Those aren't fog lights. They don't have proper beam patterns. I want to strangle everyone who uses light bars on the roadways with other traffic around.

I agree with you on people using them on roads. I've driven a few trucks with lights bars and I always treat them like high beams, turn them on when no one is coming but once you see headlights, shut them off. They are awesome for seeing the sides of the road which is really nice because I live around a lot of planted fields and I like to see deer before they jump out in front of me.

 

[littleblazer]

Hey everyone, this was pushed in my direction via a comment on my YouTube upload. I'm thinking about buying it. It is a little expensive but between the wire loom and relays it's roughly 20$ extra to buy it and I don't have to make crap work myself. The ground has me a little nervous but I suppose I could modify that.

https://www.gen5diy.com/collections...15-2018-chevrolet-suburban-foglight-harness-1

 

[gpking]

If you're comfortable with making harnesses yourself, I did mine for under $25. I really wanted to be able to use an original fog button instead of an obviously aftermarket switch, or just wiring them to the headlights.

Our fog button is a negative trigger so I just bought a $10 latching relay that had a mode that handles negative triggers.

Here is a simplified drawing of my wiring in the TrailBlazer:
PAC TR-7 Latching Relay = $9.99 on Amazon
Cheap SPST (4-pin) Relay = like $3
Add-A-Fuse = $8

 

[littleblazer]

If you're comfortable with making harnesses yourself, I did mine for under $25. I really wanted to be able to use an original fog button instead of an obviously aftermarket switch, or just wiring them to the headlights.

Our fog button is a negative trigger so I just bought a $10 latching relay that had a mode that handles negative triggers.

Here is a simplified drawing of my wiring in the TrailBlazer:
PAC TR-7 Latching Relay = $9.99 on Amazon
Cheap SPST (4-pin) Relay = like $3
Add-A-Fuse = $8
View attachment 86830

The problem isn't that I can't make it. I have everything to do it laying around. The problem is the weather pack plugs for the bulbs are unobtainium...

 

[gpking]

The problem isn't that I can't make it. I have everything to do it laying around. The problem is the weather pack plugs for the bulbs are unobtainium...

Ahhh, well I'm the nut who would find similar fogs at the junk yard, take the bulbs and connectors, then retrofit the housing for the new bulbs and splice in the new connectors.

I did something similar to an S10 Blazer to add a second turn signal bulb in the front turn signal housings which don't have a hole for a second bulb. I made my own hole for my own bulb and spliced the new connector in to the existing wiring!

 

[littleblazer]

Ahhh, well I'm the nut who would find similar fogs at the junk yard, take the bulbs and connectors, then retrofit the housing for the new bulbs and splice in the new connectors.

I did something similar to an S10 Blazer to add a second turn signal bulb in the front turn signal housings which don't have a hole for a second bulb. I made my own hole for my own bulb and spliced the new connector in to the existing wiring!

I'd do the same but they swapped bulb types in 2017 and as of right now it's a gm only type thing. I found the old style plugs but the notching is wrong. Same bulb part number sans an X lol.

 

[littleblazer]