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

[seamus2154]

Thanks Guys! All good input! The Putco harness was a real quality piece. Had a wire for reverse which I used for my relay trigger. Only had to tap into the 12v constant on the trailer harness which is the only live wire on that harness in 2021 with no trailer hooked up. Came out great, this is what forums are for...help. Thanks guys!!!

Edited August 4, 2021 by seamus2154

[Aaaaaaaayush]

Sorry Im a bit late but the reverse lights or all lighting in these trucks run through the BCM Body Control Module. Some higher power lights like the headlights have relays in the fuse boxes but those relays get their trigger from the BCM. I've added tons of LED lighting to my interior lights so when I open my door at night everything is lit, There is a limit to how much amperage the BCM can provide. It shouldn't damage anything but the BCM will trip out like a self resetting breaker it will try to start the load a few times and then give up until restarted (I found out when I wired too much to that specific output).

 

Also the light pods in the bumper step may mess with the blindspot microwave radar sensors (If equipped), i believe they are mounted behind the plastic bumper step in these T/1 trucks.

[kodiakdenali]

33 minutes ago, Aaaaaaaayush said:

Also the light pods in the bumper step may mess with the blindspot microwave radar sensors (If equipped), i believe they are mounted behind the plastic bumper step in these T/1 trucks.

 

before I did the install I tested the cross traffic alert system with the light modules in place attached with painter's tape. I went to a parking lot and waited for traffic to drive by. all of the sensors worked properly. after the project was complete with everything installed in its final position I can confirm no effect on backup or cross traffic systems.

 

The sensors are indeed mounted to the inside surface of the step pockets, but towards the rear of the vehicle. To the rear of where the light pods are installed.

Edited August 5, 2021 by kodiakdenali

[Aaaaaaaayush]

1 minute ago, kodiakdenali said:

 

before I did the install I tested the cross traffic alert system with the light modules in place attached with painter's tape. I went to a parking lot and waited for traffic to drive by. all of the sensors worked properly. after the project was complete with everything installed in its final position I can confirm no effect on backup or cross traffic systems.

good to know.

[seamus2154]

My constant 12V is off the trailer plug to the relay. The trigger for reverse is from the Putco harness that is inline to taillights then to relay. Triggers and powers up reverse light perfectly, nothing times out or trips, and no issue with cross traffic or parking sensors. The extra light does not wash out the backup camera if anyone is concerned. It adjusts to the extra light. Might be under the threshold of the BCM but works perfectly.

[GETGONE]

So I finally got to messing with my lights the other night after reading this and being disappointed the Curt RV harness I bought wouldn't work to tap the lights. I pulled the passenger tail light to see what the wires were for the bed lights and reverse lights. I built a harness from a 2 wire plug at my 2"x2" lights I mounted either side of the hitch. I used the black wire from the tail light harness for ground using T Taps. I tapped the blue wire for the cargo lights and the light green for reverse. I put diodes on both of those wires so I wouldn't get any back feed through the circuit since they combine to the positive wire of the LEDs. Now I have additional backup lights down low and can turn them on as cargo lights for hooking up a trailer or seeing behind at night if loading stuff up.

[seamus2154]

Looking good! Yep it was the light green wire for reverse. I used the Putco harness which was plug and play and had a reverse wire on plug. Made it a breeze. I was intitially taken back with the price till I received it. Very nice quality and didnt have to cut the wire. 

[GETGONE]

What did you use to plug into the other side of the reverse light wire on the Putco harness? It looked like it had an OEM type weather seal connector but only the one side and not a pigtail to splice into the other side. I'm guessing it only works with the Putco blade light.

[Goodtill]

On 7/29/2021 at 9:13 AM, Zelas said:

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

https://www.putco.com/529005

 

This is definitely what you want to use. if you try to tap into the trailer wiring harness for 12v and grd, the ecu  thinks you have a trailer hooked up and puts you in trailer mode.

 

I put a marine panel in my bed to give me a 12v cigarette plug, dual usb port and switch to turn on the additional bed lighting and had to run a power line all the way to the battery to power it.

[seamus2154]

On 9/15/2021 at 10:40 PM, GETGONE said:

What did you use to plug into the other side of the reverse light wire on the Putco harness? It looked like it had an OEM type weather seal connector but only the one side and not a pigtail to splice into the other side. I'm guessing it only works with the Putco blade light.

I was using that wire to trigger my relay, which then turned on my LED lights. So I cut the plug off and wired direct to the relay.

[kodiakdenali]

On 9/17/2021 at 6:25 PM, Goodtill said:

This is definitely what you want to use. if you try to tap into the trailer wiring harness for 12v and grd, the ecu  thinks you have a trailer hooked up and puts you in trailer mode.

 

I put a marine panel in my bed to give me a 12v cigarette plug, dual usb port and switch to turn on the additional bed lighting and had to run a power line all the way to the battery to power it.

It didnt for me, I did find that the trailer harness was useless for any other light signals, I got all of those from a putco harness, but power and ground I got from the trailer harness without any side effects.

I am interested in your marine panel mod. I have plans for more bed mods, nothing built yet though. Do you have pictures of your setup? Could be inspirational.

Edited September 20, 2021 by kodiakdenali

[GETGONE]

I had to redo my harness and add a relay after I added the GM step lights and replaced the LED's from the kit with brighter ones I found on ebay. When the cargo lights were on it would cause the lights I added to flash and go off along with the lights in the bed. I used the far side of the tapped wires with the diode as inputs to trigger the relay from either the reverse lights or cargo lights. I tapped the Curt RV harness for the 12 volt + to power the lights. Now everything works as it should.

[RedLT]

Seems like a relay is a must when adding additional bed or perimeter lights. Good to know for future projects.

[GETGONE]

Throwing my write-up from another thread here to help others:

 

I added the GM light kit for my multi-flex tailgate as well as swapped the lights to brighter aftermarket LED units. I added some 2"x2" LED cubes I had purchased for my Avalanche but never used. The current draw tripped the BCM and they would blink 3 times then go off. I also hooked the cube lights up to the reverse signal so they come on in reverse and at night when the approach lights turn on when you unlock the truck or lock it and leave. I had added a Curt 5th wheel wiring harness expecting I could get my signals from there for what I was originally wanting to do. I found on here that only the 12V+ wire has signal at all times. I pulled the tail light and looked at the wiring. I have LED bed lights in the corners from factory. I tapped that wire on the passenger side(or could use drivers side) and ran that to the 86 wire on a waterproof relay. I added a diode to it so current can't back feed to the bed light circuit. I also tapped the reverse light on the same side, added another diode here so current can't back feed the circuit and added it to the 86 wire. There is a harness that plugs in under the bed and connects to the tail lights. I purchased a new harness to keep as a spare in case I ever had electrical issues that required me to take it to the dealer. I can unplug everything I added and return it to stock. 30 wire I connected to the 12V of the Curt 5th wheel harness I added. This plugs in via T to the factory trailer plug. I have the actual 7 wire plug running into the blank in the passenger bed side where the 120V outlet would be if I had that option. 85 wire can be tapped into the trailer harness ground wire or find a suitable ground wire elsewhere on the chassis or trail light harness. 87 connects to your additional lights. I didn't add a fuse to mine since I'm using the 12V+ from the trailer harness and it is already fused. 87a is NOT used and can be removed or taped off. I heat shrunk/electrical taped up connections and then zip tied the relay to the Curt 5th wheel harness along the tail panel of the bed.

 

For those not wanting to read it all:

Waterproof relay(as shown above)

30 wire - 12V+ from trailer wire circuit

85 wire - 12V- ground to trailer wire ground, taillight ground, or other suitable chassis ground

86 wire - 12V+ input from LED bed lights and/or reverse lights, using a diode on each input wire to prevent back feeding trigger circuit

87 wire - 12V+ to your additional lights

87a wire - NOT used and can be removed from relay harness or taped off. Not all relays have this pin/wire

[AD Powell]

On 7/27/2021 at 9:04 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