Updated: Nov 8, 2020
Keep in mind, this 2015 GMC Sierra has fender flares, so the instructions may vary a little.
First start by opening the hood.
Once the hood is open, you'll find the plastic shroud cover over the grill mounting points. Use a panel pry tool to remove the "12" plastic push clips holding the shroud in place.
Notice the "4" 10mm screws holding the top of the grill in place as well as "2" top mounted screws on each headlight. These we will come back too.
If you are working with a truck with fender flares, you will need to first remove them before going further as the flares cover a front fascia trim piece that will also need to be removed.
Hardware tends to vary from truck to truck with aftermarket parts but in this case the were held on with "5" T20 screws.
Once the Fender flare, or factory trim is removed, you'll find a few T20 screws holding the inner fender liner against the front clip. Remove these screws to be able to pull the liner back some for easier access to a hidden screw. The liner does "NOT" need to be fully removed.
with the fender liner pulled back, you can now see the once hidden screw. The screw is holding the lower front fascia trim to the Fender.
Using a 7mm socket, remove the screw from the trim from both side of the truck as they are mirror images.
At this point it is safest to apply some painters tape to the fender where it meets the fascia trim to ensure no damage to paint when removing or re-installing the trim later on.
At this point you are ready to start pulling the front fascia trim from the truck. There is a plastic tab (if not already broken) in the second notch from the inner fender forward that will need to be pressed down while pulling the fascia out and forward of the truck. This will release the trim from either side and can be popped out from under the headlights.
Stop pulling here!!!
At this point it is always nice to have a helping hand however it can be done on your own.
Shown below, as you climb under the truck, you will spot tabs that are holding the front fascia trim in place across the front middle section of the grill.
With a panel pry tool, depress the clip gently as the tabs can be brittle at times, allowing the front fascia to slide out from the tab.
Sown below are additional tabs.
Once all the tabs are released, the front fascia trim can be fulling removed from the truck and set aside.
With the fascia trim removed, you can now see the "4" 10mm screws holding the bottom of the grill in place. Remove these "4" screws. You'll also find "2" 10mm screws on the bottom section of the headlight (each). Remove them as well.
With all the lower screws removed, we can now focus on the top of the grill. Remove the "4" 10mm screws holding the top of the grill in place.
Note the screw location by the clean section left behind for fitment later on.
With the "4" top screws removed, use a panel pry tool to gently lift the trim up and away from the front of the truck. This will allow for the plastic tabs to be released.
With the tabs released across the top, you'll find next to yet below the headlights on the grill "2" pop in clips visible. There are "10" total. Typically these are not a issue and the grill can be pulled from the front end of the truck. Pull the grill straight out with a gentle tug.
Shown below, one can see the "10" clip holders ( 2 top center, 4 outer sides, 4 across the bottom).
Note that the grill does have a alignment tab when re-installing.
At this point, the "2" remaining screws per headlight and be removed. Once the screws are removed, pull the headlight and disconnect the harness.
At this point, you can either swap out your headlights, grill, bulbs and so forth. In my case, changing out the headlights.
To learn more about adding a headlight harness for any 14'-18' SLE trim or lower to accept LED DRL functions, please read on...
Thanks to Gen5DIY_ for supplying the harnesses needed to adapt Chevy, Dodge, and GMC vehicles.
Shown below is the harness needed for my 2015 GMC SLE Trim truck to either run SLE/Denali Headlights or any aftermarket headlight with LED DRL's.
This harness comes with "4" relays attached to a aluminum mounting bar as well as a add fuse port, power wire, and "4" direct inline plugs. This is a plug and play setup and provides the perfect amount of wire length.
Shown below, is the drivers inner fender where I mounted the relay system, making it easy to access if ever need be, and perfect distance to fuse block. This is mounted with plenty of room to still add a secondary battery if I ever plan to in the future.
With the plug ends being a direct plug and play the rest is pretty straight forward as they only fit one way. Plug in drivers side factory harness to Gen5Diy harness, then Gen5Diy harness into the headlight. Repeat for other headlight.
Shown below is the headlight running on factory harness....
No LED DRL function.
Gen5Diy harness installed in 5 minutes now allowing the LED DRL's to fully function!
Below: Parking lights only ON.
Hope this helps with a current or future mods/repair to your vehicle!