DIY: Make 2015-2017 LS/LT headlights operate like a LTZ headlight (LED as DRL vice low beams)

[Tylus]

@Tylus very well done. I actually just built pigtail harnesses that swap these circuits so the factory forward lamp harness doesn't have to be modified. That way it's plug and play and reversible.

very nice and slick. I couldn't find connectors. Would have built something very similar if I had. I prefer your way.

1. You mentioned the Y91 forward lamp harness is larger to allow for more voltage draw. However, the wire gauge sizes are similar across the suv platforms at the headlamp connectors. The only exceptions are for those with RPO 6J7 (for PPV highbeam flasher) and the Escalade DRL circuit. Both are 18AWG instead of 20AWG in those instances. What am I missing? In 2018, when GM began using the LED strip for DRLs on all Tahoes, the main harness change I see is the wire at position 6 on the headlamp connectors only being 18AWG and only describing it as the DRL Control circuit.

Good catch. I didn't realize that the Z75 (Cadillac) was the only harness with position #6 being physically larger. I was reading that wrong.

Looks like when the upgraded the 2018 models to LTZ function, they bumped the wire size to match Cadillac

2. I also saw where you said the wiring diagram showed the LTZ LED strip being physically different. Can you expand on which diagram and where it shows that? I'm not seeing it.

Refer to Piece #13 and #14 below. The LTZ has piece #13. LS/LT has #14 (minus Y91 package)
I don't know if it's something we can retrofit or not.

​

Getting the LED strip to have the same brightness as the LTZ version is what I've been working on. What I haven't determined yet is whether the LED strip hardware is different on the LTZ or if it's the circuitry/programming on the components inside the headlamp assembly. The parts catalog I can see doesn't show anything about the LED (only HID/non-HID assembly). Like @Kpwweb mentioned, I wonder if it's a PWM control issue where bypassing it with a relay would work. Although, if that's the case, I would think Gen5DIY's $230 LED DRL harness with its relays would address it. They make a point to state the LED brightness won't change. Maybe that's all their harness does, swap the circuits and use the DRL control to activate relays to provide a constant +12v. They even give the same disclaimer on park lamp/headlamp functionality change that you noted. What are your thoughts?

Like I said above. I'm 99% positive the LTZ DRL is physically different. The Y91 electrical circuit has the logic module. And it looks like the PCM can command varied voltage to the LED strip to achieve different levels of brightness to those equipped.

The only other way I'm currently aware of to do this is with three relays. That allows the LED strip to function as DRLs and keep factory functionality with the other headlamp functions. That's the way @73Vetteman did it.

relays fail...sadly.

And I cannot remember the last time I ever needed my parking lamps and not needed the headlamps. It's a unnecessary complication that invites failure for me. Very cool though for the complete LTZ mimicry.

I'm happy to build the pigtail harnesses with or without the relays for those interested. I'll even do the install with the relays if you'll come to me so I can verify the LED brightness. I'm in Mobile, AL.

I'm not positive more voltage would help. The LED strip is already receiving nearly 12v. It's more a lumen issue. The LS/LT strip doesn't have the same lumen output that the LTZ does.

 

[Kpwweb]

@Tylus very well done. I actually just built pigtail harnesses that swap these circuits so the factory forward lamp harness doesn't have to be modified. That way it's plug and play and reversible.

...

I'm happy to build the pigtail harnesses with or without the relays for those interested. I'll even do the install with the relays if you'll come to me so I can verify the LED brightness. I'm in Mobile, AL.

I’m game for a harness, not sure on the relay part yet... I also don’t live near you, but I would buy one.

Let me know. Thanks!

 

[cmatt]

I’m game for a harness, not sure on the relay part yet... I also don’t live near you, but I would buy one.

Let me know. Thanks!

Sent you a PM.


Sent from my iPad using Tapatalk

 

[fozzi58]

....I'm not positive more voltage would help. The LED strip is already receiving nearly 12v. It's more a lumen issue. The LS/LT strip doesn't have the same lumen output that the LTZ does.

I have a 2017 LS and there are 2 spots on the LED strip that have brighter LEDs than the remainder of the strip. I will see if I can pick out a picture tonight. That might confirm a different part or possibly show that the voltage is dropped to reduce the brightness.

You obviously have a much higher understanding of the electrical system than most of us here. Any assistance with the upfitters guild would be appreciated. I would like to add some features to my truck such as the Caddy mirrors with the power fold etc (no 360) so knowing what part numbers to purchase and what fuses to add would be very helpful.

I would also be interested in the harnesses for the DRLs since the kit available from Gen5DIY is still $200+

 

[mdravc]

I’m game for a harness, not sure on the relay part yet... I also don’t live near you, but I would buy one.

Let me know. Thanks!

I'm also interested in the harness you built-- let me know as well!

 

[cmatt]

I have a 2017 LS and there are 2 spots on the LED strip that have brighter LEDs than the remainder of the strip. I will see if I can pick out a picture tonight. That might confirm a different part or possibly show that the voltage is dropped to reduce the brightness.

You obviously have a much higher understanding of the electrical system than most of us here. Any assistance with the upfitters guild would be appreciated. I would like to add some features to my truck such as the Caddy mirrors with the power fold etc (no 360) so knowing what part numbers to purchase and what fuses to add would be very helpful.

I would also be interested in the harnesses for the DRLs since the kit available from Gen5DIY is still $200+

I can help with the Escalade mirrors and DRL harness. Send me an email to cmattbuild1 AT gmail DOT com so not to clutter up the thread.

I'm also interested in the harness you built-- let me know as well!

Send me an email to the addy above.

 

[Tylus]

Another unrealized consequence of doing this. This is essentially the 6 light mods for the 2015+ models.

When the high beams are turned on, the low beams and fog lights remain powered

FYI for those who get inspected and/or worry about such things.

 

[RST Dana]

Another unrealized consequence of doing this. This is essentially the 6 light mods for the 2015+ models.

When the high beams are turned on, the low beams and fog lights remain powered

FYI for those who get inspected and/or worry about such things.

Hopefully it does not change anything with the auto dim feature.

 

[Tylus]

Hopefully it does not change anything with the auto dim feature.

Nope. All of my auto dim functions worked great this morning

 

[dvpvic]

Well I’m new on here just got the wife a 2016 LT well equipped. I was looking up LED/HID options and stumbled on this LED DRL thread and done little research. I had a friend that has a set of 2018 non HID headlamps and swapped them in to see if they will work direct plug and play. Here’s what I found; on my rig DRL seems to be the led strips only. I don’t have any other lamps come on when in gear D/R etc. I then swapped in a single 2018 unit and left one original one. Attached is a pic that shows the brightness difference. I also took 12v directly to each unit and they lit up as the function while on vehicle which shows that’s there’s no funky pwm going on. Not sure if I have some kind of mod. It come from a family that had it serviced at dealers etc so no one did any mods to my knowledge. I have RPO codes X88 and Y86 I think one of these is tied with the DRL option that I saw OP post about. Anyone know what I’m missing? Anyone on here have a 15-17 that could describe how their DRL functions? Because I think I’m just going to keep the 18’ set on and have the brighter LEDs. You can also see a slight color shift towards the cooler spectrum on the brighter LED




Sent from my iPhone using Tapatalk