Wiring for the TB Fog lamps

roamingphantom

Original poster
Member
Apr 1, 2012
10
Hey folks,

Without trying to be a dickhead (lol). I was wondering if anyone have the diagram of the wires on the TB fog lamp. I have the ls which didnt come with the fog switch, i just bought the one with it on and wanted to know how to wire it up.

Also if anyone have an OEM harness or know where i can get one online or in nyc i can take that too.

Thanks very much..
 

Sparky

Member
Dec 4, 2011
12,927
You're going to be better off custom wiring it. The BCM controls all that stuff in these trucks, and since you have the LS (Like I do) the BCM has been programmed for no fogs. Your BCM will completely ignore the fog light switch unless you get it reprogrammed, which costs $$$ and frankly IMO it isn't worth it :frown:

Eventually I want to put fogs on my LS, when I do I'm going to go with the classic switch and relay setup. I'll just cut a spot for my aftermarket fog switch in the blank area.
 

roamingphantom

Original poster
Member
Apr 1, 2012
10
so you are saying i cant use the switch that i bought? Damn Damn Damn. I wanted to have that oem stock look. Is ther any way around it - about how much would the bcm reporgram cost?
 

Sparky

Member
Dec 4, 2011
12,927
There is probably a way to do it. Is it a momentary button or does it latch on and off? If you found which wires go to that switch, you could then cut and reroute them to the aftermarket fog relay. If it is a momentary switch, you'd need a latching relay.

So yeah, it can be done, tho it does require snip-snip on a few wires. According to my diagram the orange wire going into the headlight switch unit goes to the fog switch. The dark green/white wire looks to be the illumination for the switch (it is a ground wire, the BCM grounds the factory fog relay to turn it on).

Make sure that if you do go this route that you don't just tap into the fog light switch wires, but actually cut them. You don't want to backfeed the BCM by accident!
 

roamingphantom

Original poster
Member
Apr 1, 2012
10
I dunno if its momentary or not - here is a picture

List: Fog Lamp Switch - 2004 Chevrolet Trailblazer | O'Reilly Auto Parts

Its the push in one on the right side.

oh before i forget. I am not doing this myself - someone else is, since i know diddly squat about car wiring.

Before i forget also. I already have the fogs installed and a cheapo aftermarket ugly looking switch there. It works just fine. I thought it was just a matter of taking those wires and hooking it to the OEM switch and like magic it would work with the oem assuming there were 3 wires - like ther are 3 pins on the oem switch.
 

Sparky

Member
Dec 4, 2011
12,927
Easy way to find out - push it and see if it clicks and stays pushed inward :biggrin:
 

Sparky

Member
Dec 4, 2011
12,927
You'd need a latching relay then if you wanted to use the button.
 

roamingphantom

Original poster
Member
Apr 1, 2012
10
Sparky said:
You'd need a latching relay then if you wanted to use the button.

I googled it but found many. Can you point me to exactly what i need and i can pick it up.

Here is a pic of the harness i wanna use
 

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The_Roadie

Lifetime VIP Donor
Member
Nov 19, 2011
9,957
Portland, OR
The latching relay function you need involves having a special relay, or some circuitry designed and built surrounding a normal relay. Just finding a wiring harness that involves a relay socket won't be enough. You need an experienced electrical designer. There will be no plug-n-play product that does exactly what you need done.
 

Sparky

Member
Dec 4, 2011
12,927
What Roadie said.

How good are you with electrical stuff? This is going further than what I'd recommend a beginner do, simply because if you cut the wrong wire or tap the wrong wire you could backfeed the BCM or make something else not work. That wouldn't be cool :no:
 

Ace1875

Member
Mar 29, 2012
276
roamingphantom said:
I googled it but found many. Can you point me to exactly what i need and i can pick it up.

Here is a pic of the harness i wanna use

those are HID relay kit


There are several options. First, you could wire them to any of the lights already present in the front with a relay. Second, you could utilize the fog light relay and fuse that are already in the fuse box under the hood. Thirdly, you could pull wires through the firewall.

The first option is definitely the easiest. All you have to do is add a T-tap to the correct wire, in our case we connected the fog light control to the (+) low beam. Then connect this T-tap to the coil on the relay and ground the other side. At this point you would need power for the fog lights which will be switched by the relay that was just described. The fuse box under the hood has a simple spot where you can simply add a ring with a wire to connect to battery (+). In this wire I suggest you add fuses. We used a 20amp fuse. Now the second wire you need is ground. You could connect this to the frame or the battery itself. Make sure that you can get a good contact and always test the ground after you install it with a multi-meter. This method allows you to have the fog lights automatically come on with the low beams

The second option is a bit harder, however this would allow you to make it look more stock. You can solder on the bottom of the fuse box the wiring for the fog lights, everything should be present except for the wiring harness to the fog lights. After you've connected the fog lights to the fuse box you have several options for how to control them. At the BCM you could connect the fog light relay control with the low beam relay control, this would essentially work the same as method one, except you connect the low beams and fog lights at the BCM. The other option is that you buy the stock headlight switch with fog light control. This will not work straight out of the box, to have it work completely OEM the dealership has to reprogram the BCM so that it will interpret the fog light signal and switch the fog light relay control accordingly. However, one could just cut the fog light relay control @ the BCM and T-tap it to the fog light control signal. This way the BCM does not have to be reprogrammed, plus the fog lights will then not turn off when you turn your high beams on. If you do want your fog lights to turn off when your high beams turn on, just add a relay and connect the relay's coil to the high beam relay control

The third option is very similar to the first option, except instead of using a light signal, we pull 1 or 2 wires through the firewall and put a switch behind it, this will look the least OEM of them all. You can however, get the OEM light switch with fog light control and wire the fog light signal to a relay to control them behind the dash and pull the wires for this through the firewall. This would work the same as the second option, this way you don't have to mess with the wiring at the BCM. However, this way you do have to pull 1 or 2 wires through the firewall.

View attachment 20131
wiring_overview.jpg

This is a quick overview of how we need to wire the headlights. You have to connect the right fog lights (left in the picture) to the left side of the car (right in the picture). We did this by guiding the wire up to the right headlight (left in the picture) and then guiding wire along the existing light wiring harness it through the tube right behind/below the grill to the left side of the car (right in the picture). The left fog light is pulled up the headlight wiring on the left (right in the picture). Both of these fog lights are then spliced together and connected at a relay. This relay is switched via the low beam signal which in turn can connect the battery (+) to the fog lights when the low beams are on. The ground is always connected. For the low beam signal, check the wires on the connector on the headlights and test with a multimeter which is the low beam signal wire
wiring_relays.jpg

At the left headlight connector we connected a green wire to the low beam signal, we then connected this to the connector allowing us to disable the fog lights if needed simply by disconnecting this connector. (You can see this connector right above the left headlight connector). This signal then leads to the coil on the relay and the other side is connected to ground (leads off to the right along with the batt(+) between the fender and the battery to the fuse box under the hood. The left and right fog lights are spliced together and are connected directly to ground and the other side is connected to the switched battery(+) on the relay.
wiring_b_g.jpg

This is between the battery and the fusebox under the hood. You can see where the wire connects to the battery (+) under the fusebox cover, and the ground connects to the bolt against the fender.

-Source: ewoutvb.com
 

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roamingphantom

Original poster
Member
Apr 1, 2012
10
This is fantastic information - i am gonna go to a shop that i trust to do this one. I thought it was a plug and play situation - well shows how much i know.

I REALLY REALLY APPRECIATE ALL THE HELP YOU GUYS PROVIDED!!! Cheers (Not shouting, just emphasizing)
 

Ace1875

Member
Mar 29, 2012
276
roamingphantom said:
This is fantastic information - i am gonna go to a shop that i trust to do this one. I thought it was a plug and play situation - well shows how much i know.

I REALLY REALLY APPRECIATE ALL THE HELP YOU GUYS PROVIDED!!! Cheers (Not shouting, just emphasizing)


no prob. now if u want your BCM to control the fog lights the Fog light relay control wire is "dark green with white" Pin Number E11
Fog light Switch signal wire is orange Pin F6.

e11 from BCM will connect to 86 on relay. then the factory switch should automatically work
 

Mooseman

Moderator
Dec 4, 2011
25,178
Ottawa, ON
If you download the manuals (link in my signature), I'm sure that info is in there.
 

Mooseman

Moderator
Dec 4, 2011
25,178
Ottawa, ON
I just downloaded it, no problem and I'm not even at home over cellular. I attached it here but I can't do it for the majority of them because they're too big.

Be sure to use the proper user name and password as specified in the first post in the thread, not your GMT Nation login.
 

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addukes82

Member
May 13, 2023
8
Utah
I just downloaded it, no problem and I'm not even at home over cellular. I attached it here but I can't do it for the majority of them because they're too big.

Be sure to use the proper user name and password as specified in the first post in the thread, not your GMT Nation login.
Thanks man. Yea I tried the 2008 and screen flashed but no download after I entered info.
 

Mooseman

Moderator
Dec 4, 2011
25,178
Ottawa, ON
Try doing a right click and "Save as...". Some browsers don't like the links. I have no problems with FireFox.
 

addukes82

Member
May 13, 2023
8
Utah
Try doing a right click and "Save as...". Some browsers don't like the links. I have no problems with FireFox.
Yea was only letting me save 1. Then hold click save link and works flawlessly. Thanks man.
All wired up, then a Last min change of bypassing bcm , don't think it would work and not gonna reprogram. Maybe once I grab a tech2, it's wired and ready for it tho. Went ahead and added another set of fogs (X4) for shits and giggles. So just got to wire relay and showtime
 
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