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2021 Sierra -wiring LED backup lights...electrical experts needed!

seamus2154
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seamus2154 Enthusiast

seamus2154

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Hey Guys! I have a New 2021 Sierra Denali 3.0 Duramax. Love it so far and have been sorting it out nicely. I have had 3 of the previous generation truck. I always mount LED rear backup lights on the rear bumper as some of the places I race have no lights in the parking lots. In the past I pull 12V power and the reverse light as a trigger wire for the relay for the lights, off the trailer wire connector. Well.......this 2021 does not light up that plug unless the trailer is connected. Once you plug in the truck recognizes a trailer is hooked up. For some reason there is 12V that is on but none of the other wires are live till a trailer is hooked up. I thought something was wrong so  hooked up the trailer and boom everything then works and the display states trailer hooked up.  So...I can get the 12v for the relay but now I am trying to find which wire on the rear tailight harness is the reverse lights? Appears to be the light green one I think?? But this truck is all LED and its a very light gauge wire. Does this truck have a LCM like the german cars.? Light control module. Will it sense a larger load and screw up something?? Pretty common with german cars. Also afraid to mess up any modules? I have wired 10 different pickups this way but the new generation is definetly different! Any advice for a trigger wire on relay?? Is that much of a load to the relay??

 

Thanks

Edited by seamus2154
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seamus2154
seamus2154

Hey Guys! I have a New 2021 Sierra Denali 3.0 Duramax. Love it so far and have been sorting it out nicely. I have had 3 of the previous generation truck. I always mount LED rear backup lights on the r

Enough
Enough

I went another route since I didn't want to take a chance cutting and splicing wires.  I bought Curt Industries T-connector 56584 and flat wire extension 58531. The T-connector t's into the big bumper

Transient
Transient

There are some electrical plugs up by the spare tire that allow for the Putco blade tailgate led lightbar to work.  I have that accessory and did the install.  It was plug and play.  The lightbar does

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seamus2154 Enthusiast

seamus2154

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No one knows if this truck has a module running the trailer plug or rear taillights ?? Nervous to just use that light green reverse tailight wire as a trigger for the relay and destroy a module. 

This is the stuff I hate about my German cars, cant mod a thing without a computer problem. 

jashaw Enthusiast

jashaw

Posted
Posted

I have a tailgate LED light bar, and light strips that use power directly from the reverse lights. I will have to see what wires I used since it's been a while.

 

Not sure if they're the same as my 2020 RST though.

Enough Enthusiast

Enough

Posted
Posted

I went another route since I didn't want to take a chance cutting and splicing wires.  I bought Curt Industries T-connector 56584 and flat wire extension 58531. The T-connector t's into the big bumper wiring harness behind the bumper and the extension plugs into the T-connector. I then connected my aftermarket reverse lights to the extension. This way nothing in the truck's original wiring is altered.

 

This setup also gives me the option to connect other running lights or turn signals using the remaining wires on the extension with no worry about the trucks original wiring.

 

https://www.curtmfg.com/catalogsearch/result/?q=+56584+Trailer+Wiring+Harness

 

https://www.curtmfg.com/part/58531

 

I bought some cheap Nilight lights from Walmart in case this idea didn't work so I've got less than $75.00 in this setup. The lights are plenty bright but don't wash out the camera at night.

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seamus2154 Enthusiast

seamus2154

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Thats a great option for not cutting the wires, thanks. I dont know if the 2021 Sierra Denali is different that the trailer plug is not active other than a 12V when a trailer is not plugged in. None of the pins light up without a trailer plugged in. Never came across this before. I assume its due to the new trailer package and interaction with the screen?? So if that plug is not live I cant see how the T would work on the 2021???? As soon as the trailer is plugged in, it pops up on screen and prompts for the light test which works perfectly and all trailer lights work. Unplug it and test those pins and nothing but the 12V works. There is a schematic on the plug cover if you look. So i am assuming its going through a module???? 

Thnaks for the input

Transient Senior Enthusiast

Transient

Posted
Posted

There are some electrical plugs up by the spare tire that allow for the Putco blade tailgate led lightbar to work.  I have that accessory and did the install.  It was plug and play.  The lightbar does illuminate white when put in reverse.  Perhaps you could create a harness to work between both ends of the plugs.

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Zelas Enthusiast

Zelas

Posted
Posted
On 7/27/2021 at 10:04 PM, seamus2154 said:

Hey Guys! I have a New 2021 Sierra Denali 3.0 Duramax. Love it so far and have been sorting it out nicely. I have had 3 of the previous generation truck. I always mount LED rear backup lights on the rear bumper as some of the places I race have no lights in the parking lots. In the past I pull 12V power and the reverse light as a trigger wire for the relay for the lights, off the trailer wire connector. Well.......this 2021 does not light up that plug unless the trailer is connected. Once you plug in the truck recognizes a trailer is hooked up. For some reason there is 12V that is on but none of the other wires are live till a trailer is hooked up. I thought something was wrong so  hooked up the trailer and boom everything then works and the display states trailer hooked up.  So...I can get the 12v for the relay but now I am trying to find which wire on the rear tailight harness is the reverse lights? Appears to be the light green one I think?? But this truck is all LED and its a very light gauge wire. Does this truck have a LCM like the german cars.? Light control module. Will it sense a larger load and screw up something?? Pretty common with german cars. Also afraid to mess up any modules? I have wired 10 different pickups this way but the new generation is definetly different! Any advice for a trigger wire on relay?? Is that much of a load to the relay??

 

Thanks

This Is what you want to use. Its plug and play with reverse out.

https://www.putco.com/529005

 

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seamus2154 Enthusiast

seamus2154

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2 hours ago, Zelas said:

This Is what you want to use. Its plug and play with reverse out.

https://www.putco.com/529005

 

Wow, this looks perfect! I put in 2021 and it states it does not fit a 2021 Sierra 1500!!! I am going to call them

 

Thanks for your help, hoping website just isnt updated to 2021? 

kodiakdenali Enthusiast

kodiakdenali

Posted
Posted

I actually just finished a project to add several different lighting systems to the back of my truck. for mine I used a curt adapter for the 7 pin trailer harness and a putco harness intended for tail light bars. I cut up both harnesses and customized them for my exact application, using the curt harness to get 12V and ground and used the putco harness to trigger relays. the backup lights signal to the rear tail light activates a relay which connect power from the 7 pin harness to a set of LED light pods which I have integrated into the corner step pockets. This approach worked very well.

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seamus2154 Enthusiast

seamus2154

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UPDATE:

 

As per Putco the 2021 is different as far as the trailer plug lighting up without a trailer plugged in. The 2021 needs to see the constant draw from the trailer. 

The good news is this blade harness WILL work as needed!!!! Thanks Transient !Thanks Zelas !   BIG Help!!!!

  • Like 1
Stove09 New Member

Stove09

Posted
Posted

I am having this same issue right now. I mounted two 7" led bars to the bottom of the bumper and wired them into the trailer harness like I did on my last 2 trucks (green with white strip for reverse power and solid white for neutral) but they wouldn't work. I tried putting the truck in trailer mode and still nothing because the trailer isn't actually connected. 

Does anyone know which wires to tap into on the taillights are the power for the reverse? they seem to be pretty easy to tap into from under the truck without removing the lights and I do not want to buy a harness that cost more that the lights. 

Stove09 New Member

Stove09

Posted
Posted

problem solved. I tied the power into the light green wire and neutral into the black wire coming off the harness from one of the rear tail lights. For everyone spending over $50 on a wiring harness, on top of whatever they paid for their lights... I spent $30 on 6" double row LED lights, plus electrical tape and some extra 18 guage wire. no need to break the bank on this project!

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seamus2154 Enthusiast

seamus2154

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Happy it worked! I ordered the Putco plug in harness which will get me the trigger for the relay on backup lights. I dont know if it will have a constant 12V but can still tap the trailer plug as that has 12v only. I mounted the lights just awaiting harness. I did use a test light in the taillight harness and it seemed to be the light green wire as you said. My concern was it was very light gauge i assume due to the LED not needing much??

 

The Putco harness was more money than the LED light pods!! LOL 

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