'18 factory LED headlights and factory harness on '14 Sierra 1500

[Bono]

I did a full front end swap from a 2018 Sierra Denali onto a 2014 Sierra SLT.  I'm having issues with the low beams staying on when running.  I used the 2018 body harness so I could directly plug the 2018 headlights in.  Everything works EXCEPT for the low beams.  When the truck is not running, I can turn on the low beams just fine.  When I start the truck through, the low beams will come on and turn off after 1-2".  I tried to wire in a resistor to each one and it made no difference.  I'm wondering if I need an additional resistor, maybe 1 isn't enough?  I also wired it to the yellow and ground wires respectively.  I don't think it would matter if I wired it inline with the yellow wire only.

Edited April 30, 2025 by Bono

[Bono]

Bump, low beams won’t stay on when engine is running.

[newdude]

On 2/7/2025 at 12:35 AM, Bono said:

I did a full front end swap from a 2018 Sierra Denali onto a 2014 Sierra SLT.  I'm having issues with the low beams staying on when running.  I used the 2018 body harness so I could directly plug the 2018 headlights in.  Everything works EXCEPT for the low beams.  When the truck is not running, I can turn on the low beams just fine.  When I start the truck through, the low beams will come on and turn off after 1-2".  I tried to wire in a resistor to each one and it made no difference.  I'm wondering if I need an additional resistor, maybe 1 isn't enough?  I also wired it to the yellow and ground wires respectively.  I don't think it would matter if I wired it inline with the yellow wire only.

 

 

Wasted your time swapping the wiring when you just needed this - 14-15 Sierra SLT to 2016-2018 1/2 Ton SLT LED Headlight Harness – Gen5DIY

 

My guess is if you just plugged in the 18 harness to your 14 that there is incorrect wiring somewhere there.  Swap your original wiring back in and get that adapter harness and be done with it.  

Edited April 30, 2025 by newdude

[Bono]

The harness swap keeps all of the factory plugs for parking sensors, for lights, etc.

 

The $400 harness is just an adapter with resistors to make the different plugs match. I’m trying to sort out where those need to be added.