Aux LED back up lights error

RunGMC19 · February 21, 2022

I just installed 2 LED back up lights on my 2019 Sierra 1500 SLT. I tapped the power off of the cargo lights instead of the reverse lights so I can turn them on and off at will. When I connected the first light and tested it, it worked fine. When I connected the second light, they all (bed lights too) flashed 3 times then turned off. Has anyone discovered a work around for this configuration?

gemarsh · February 21, 2022

A 12v relay.

RunGMC19 · February 22, 2022

9 hours ago, gemarsh said:

A 12v relay.

Ok thanks, easy enough, just not sure where I'm going to find a constant 12v power supply at the back bumper. Run a wire all the way up to the battery?

GETGONE · February 22, 2022

The 12V positive in the trailer harness is hot and you can pull power from there. I had to add a relay because I added 2 2" cube lights on the hitch and brighter LED lights for the Multi Flex tailgate lighting. I have them wired with diodes so they don't backfeed the normal circuits. I have them hooked to the reverse lights as well as the cargo light circuit.

RunGMC19 · February 22, 2022

32 minutes ago, GETGONE said:

The 12V positive in the trailer harness is hot and you can pull power from there. I had to add a relay because I added 2 2" cube lights on the hitch and brighter LED lights for the Multi Flex tailgate lighting. I have them wired with diodes so they don't backfeed the normal circuits. I have them hooked to the reverse lights as well as the cargo light circuit.

Oh, nice. So you added the diode between the cargo light circuit and the relay trigger, right? Is that essential, or just for safety sake?

GETGONE · February 23, 2022

I used it because I'm using two different inputs on the same trigger terminal of the relay. I don't want to backfeed the other circuit when one is on. I don't know for sure it would cause an issue, but with how picky the electrical systems are on CAN bus vehicles, better safe than sorry. I pulled the signals from the wiring harness from the tail light to the plug under the bed. I purchased a replacement wire harness so should I ever need to take it to the dealer for any reason, I can pull the added wiring out and put it back to stock.

RunGMC19 · February 23, 2022

2 hours ago, GETGONE said:

I used it because I'm using two different inputs on the same trigger terminal of the relay. I don't want to backfeed the other circuit when one is on. I don't know for sure it would cause an issue, but with how picky the electrical systems are on CAN bus vehicles, better safe than sorry. I pulled the signals from the wiring harness from the tail light to the plug under the bed. I purchased a replacement wire harness so should I ever need to take it to the dealer for any reason, I can pull the added wiring out and put it back to stock.

Oh nice! Thanks for all the info! That's a great idea. I think I'm just gonna stick with the cargo light circuit for now so i can control them at will.

GETGONE · February 24, 2022

I can do both. Control them with the cargo light switch and when I put it in reverse they come on. Also when unlocking at night they come on since the reverse lights come on to light up behind the vehicle.

JH Architect · May 16, 2023

Wade, would you be willing to share the harness, diodes and relays you used? Also, I have heard that adding voltage draw for the LED cube lights can set off error codes. Have you had any since installing the cube lights? I want to do the same for my 2019 trail boss but I am afraid of the potential error codes.

GETGONE · May 16, 2023

This is the write-up I did in another thread on here somewhere. The dealer said my truck had a bunch of body codes when they were scanning it when I got a low oil pressure message several months ago. Those may have been from when I was trying to install an aftermarket remote start with an extended range remote though. I removed the remote start and just left it with the factory one. I don't have anything that will read the body codes in this new truck. I don't get any error codes on the display with my setup though.

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 10 amp 1000 volt 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 10 amp 1000 volt 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 tail 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

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 10 amp 1000 volt 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