DRL Disable with Auto Headlights

Midnyteryder196

Original poster
Member
Dec 13, 2013
1,490
Osceola,Ia
DRL Disable with Auto Headlights

This write up will be to disable the DRL function. This method uses a relay spliced in at the bcm and will disable the DRL, along with keeping the auto headlight function, but It will also disable the low beam's night time perimeter lighting function while remote lock/unlocking. Disabling the DRL is beneficial when installing HID low beams as the pwm signal of the DRL decreases the life of the ballasts.


Summary: Disabling DRL while retaining Auto Headlight Function
Difficulty: Easy to Moderate
Estimated Time: 30-45 min
Total Cost: $10-$20

Required tools:
Wire stripper/cutter
Crimper
2x red butt connectors
2x red scotch lock connectors
1x 4 pin relay, preferably with relay socket to make installation cleaner
4x Random lengths of wire with a female spade connector on one end of each wire if not using a relay socket

Note: Being we are going to be working on the bcm connectors, if you are not comfortable with electrical wiring then find someone who is comfortable doing it. The author takes no responsibility if you mess up the wiring, or worse yet the bcm. Also as like any electrical modifications, DISCONNECT battery before preforming any work on the electrical system.

We will be using this diagram to install the relay into the wires at the BCM.
Also the relay socket I am using has the wires color matched to the BCM.
Trailblazer DRL Disable.jpg


1. First we have to access the BCM. Short wheelbase models will need to pull up on the rear driver side seat to expose the fuse box cover, and then remove the cover off the fuse box and BCM. Long wheelbase models will need to remove the driver side second row seat to gain enough access to the BCM, once the seat is removed you will be able to take the cover off of the fuse box to access the BCM.
2. Once we have access to the BCM its time to disconnect both plugs on the side of the BCM (a gray plug, and a tan plug). From here you will need to remove some of the tape around the wires to give you enough room to cut and tap into the wires we need to.​
3. Find the pink/white wire in pin A5 of the gray plug. Follow the wire back about 3-4 inches and CUT then strip the ends of each of the wires.​
4. Next we will use a butt connectors to connect the pink/white wire from the BCM to pin #30 of the relay, and the pink/white wire that goes into the wire harness to pin #87 of the relay.​
DRL Install 1.jpg

5. Next we will find the white wire in Pin B6 of the gray plug. Follow the wire back about 3-4 inches away from the plug and use the scotch lock to connect the wire to pin #86 of the relay

6. Finally, on the tan plug find the pink wire in pin E7. Follow that wire back about 3-4 inches from the plug and use the scotch lock to connect the remaining wire to pin #85 of the relay. When done it should look similar to this.​
DRL Install 2.jpg
Once all connections are made, plug the relay into the socket, connect the battery and make sure the DRL is disabled. Once everything checks out, find a secure place for the relay, install the fuse box cover, and replace the rear seat.


.​
 

l008com

Member
Feb 19, 2016
886
Massachusetts
So if I read this right, what this does is only allow the low beams to come on when the Headlamp On Indicator Control is powered? What is that exactly?

I was under the impression that my DRL's were low power high beams, which makes this even more confusing. But maybe I'm wrong and on this truck DRL's are low power low beams?

Also if the relay used has the pin for the 'off' switch (87a), would that extra pin work as a custom, full 12v (no PWM) powered DRL that would turn off when the headlights went on?

So say I do an HID retrofit here, I'll need to kill the factory DRLs. But say I want to add my own custom LED DRL's that would be powered with ignition power, but relay-switched off when the low (or high) beams came on.
 

Matt

Member
Dec 2, 2011
4,019
The DRL's are the low beams run at about 70% of power, hence the need to either disable the DRL or do the capacitor mod to run them at 100% if you retrofit HID's.
 

l008com

Member
Feb 19, 2016
886
Massachusetts
I have a question. I was planning on using the 87a pin on this relay to power my LED DRLs. But then I realized, this is just a signal wire, not a power wire. Is there going to be enough power in there to run these lights directly? Or do I need to have the 87a pin trigger yet another relay that will run these DRL's directly off the battery or some other power source? It looks like the power consumption is about half an amp per light, or about 4.5 watts per light (two lights total of course).
 

l008com

Member
Feb 19, 2016
886
Massachusetts
Ok so today I connected a very low power yellow LED to the 87a pin on this relay. Logic dictates that whenever my headlights are OFF, and the truck is running, the little LED should be on. It's the obvious, natural choice as the trigger for custom DRL's to replace factory DRLs.

But much to my surprise, while this mod and relay work great to control the headlights as expected, I have not been able to get the yellow LED to light up at all. It's just a single straight wire going right from the lead on pin 87a, to my center console where it connects right to the led. Then the other lead on the LED is grounded.

I tried the light both ways directly off the battery before wiring it up, and it lit up both ways. So I know the LED is good and is not polarity-dependent. I guess the only real options here are:

1) The relay is bad and the 87a pin doesn't work, but the rest do
2) the solder joint between the relay's harness and the wire I ran to the center console is bad. But thats unlikely, the soldering went well and I used a ton of it and its basically impossible for it not to be getting a connection.
3) There's a break in the wire I used. This is very unlikely. It's a brand new, quite thick wire. Even if there is some broken copper, its extremely unlikely that theres such a massive break that there is on conductivity at all.

None of these seem likely. Is there something else that might be going on? Maybe I'm misunderstanding how some part of this puzzle should work?
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
I was planning on using the 87a pin on this relay to power my LED DRLs. But then I realized, this is just a signal wire, not a power wire.

This is your answer right here. My recommendation would be to buy a cheap volt meter, if there's a Harbor Freight near you, they're like $5. Then you could confirm how much voltage is there. Likely a 5V reference signal.

For the relay turning your LED DRLs on, you need to feed a 12v source to pin 30, and THEN 87a would properly power your LEDs. To keep things cleaner, you could substitute a DPDT relay, to have the additional contacts, triggered from the same source.

90050
 
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l008com

Member
Feb 19, 2016
886
Massachusetts
AHhh I didn't know that the signal wires were 5v, i thought everything was 12v. That would explain my led indicator light not turning on too!

Since I already have a regular relay running the headlights/drl killer, I could still just run the 87a lead off to another regular relay, right? Its a lot of relays but I have a bunch of them, they came in a four pack. Might as well use them all vs buying a double.
 

Mektek

Member
May 2, 2017
656
FL
You can use a small light duty relay since you're just switching a small signal to the solid state headlight relay. No need for a heavy duty 30A relay.
I think the signal wire is 12v since we have a 12v relay connected that would not activate with only 5v.
 

l008com

Member
Feb 19, 2016
886
Massachusetts
I haven’t done anything since my last post, I wanted to verify that I am getting voltage off of pin 87a before I wire anything up. But, I have not been able to get any reading off of pin 87A, under any circumstances. For example, right now there’s not a cloud in the sky, and yet with no headlights or daytime running lights on, I still get no voltage over pin 87A. This mod has worked perfectly, my headlights are coming on and off when they’re supposed to. Which is why I don’t understand why I never get any voltage off of 87A. Any ideas on that?
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
I'd test the relay for contunuity between pins 30 and 87A, when running power across the coil. Make sure there's an actual connection there. Maybe you've got a bad relay...
 

Blckshdw

Moderator
Nov 20, 2011
10,665
Tampa Bay Area, FL
Maybe... Probably. Wasn't looking at the diagram. Need to make sure it's there with pin 30 during whichever state you need it in.
 

l008com

Member
Feb 19, 2016
886
Massachusetts
Well that's the thing, when powered, pin 87 is getting power and thus this hack and my headlights are coming on when they should. But when the hadlights are not on, 87a should get power, but it's not. I can check the relay and i have a few others in my tookbox i can swap out
 

l008com

Member
Feb 19, 2016
886
Massachusetts
Checked relay, confirmed working correctly. I guess the original relay on this mod just doesn't work the way I would want it to. Given that, what do you think is the best way to power some LED DRLs?

The simplest way would be to run them off a relay connected to the battery directly, triggered by ignition power.
But even better would be DRLs that come on with ignition power, but then turn off with headlight power. So for that, I guess i'd need the first relay for power, and then pass that power through another relay, on pin 87a, triggered by the headlight power. Which I guess could be the same pink/white wire from the original mod. This might be getting a little overly complicated.
 

Midnyteryder196

Original poster
Member
Dec 13, 2013
1,490
Osceola,Ia
I've done that setup before.. check out this thread to help ya out..

 
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