Need diagram and wire code explain of rear tail light

jim larson · June 17, 2020

Well nothing I been able to find on the internet seems to match my rear tail light harnesses. I have a 2017 silverado crew cab LTZ with the factory pick up bed lighting.

I am trying to hook up the 3rd tail light and dome light of the topper I recently bought.

My tail light assembly only has two bulbs, one for the back up light and one for everything else. Back up branches of the light harness and is easy to twist to remove and replace the bulb.

The other one is a bear. There is a RED tab that I think has to be pulled out. Right? And then how does the rest of it come out? Definitely no twist and turn. This connector has a bunch of wires for everything else. I don't know which wires to use to hook up the back-up light. I need an explanation for each color wire. Every other housing I look at on the internet is different.

There is also a separate harness with two wires that go the the bed lighting. I think I can just splice the dome light into these two wires; but don't know which is hot and which is ground.

jim larson · June 17, 2020

Well getting to be more of a pain. Just got off the phone with the service department. And no help as to the color code. They did offer me an opportunity to bring in the truck and they wood wire it at the accessories rate plus parts. I mentioned that I had some wiring experience and would tackle the job myself.

slj2008 · June 17, 2020

Do you have a photo ( back of topper lamp or wire colors ) that might help you ?

newdude · June 17, 2020

1 hour ago, jim larson said:

Well nothing I been able to find on the internet seems to match my rear tail light harnesses. I have a 2017 silverado crew cab LTZ with the factory pick up bed lighting.

I am trying to hook up the 3rd tail light and dome light of the topper I recently bought.

My tail light assembly only has two bulbs, one for the back up light and one for everything else. Back up branches of the light harness and is easy to twist to remove and replace the bulb.

The other one is a bear. There is a RED tab that I think has to be pulled out. Right? And then how does the rest of it come out? Definitely no twist and turn. This connector has a bunch of wires for everything else. I don't know which wires to use to hook up the back-up light. I need an explanation for each color wire. Every other housing I look at on the internet is different.

There is also a separate harness with two wires that go the the bed lighting. I think I can just splice the dome light into these two wires; but don't know which is hot and which is ground.

There is a preferred set of instructions for wiring a topper CHMSL that GM has. GM has a dedicated circuit for powering them that involves no need to ghetto splice or scotch lock existing wiring. Also, LTZ tail lights are LED except the reverse light, so the one connector does go to a bulb, the other plugs into the LED board that is in the lamp.

Quote

2016-2019 model years

Perform the following recommendations based on vehicle configuration:

For vehicles built WITH Under Rail Bed Lighting Option:

Trucks equipped with the under rail bed lighting option will already have the female side of the X400 connector. Obtain an appropriate length of 18 ga wire to run from the X400 connector up to the CHMSL wiring for the cap or topper. Use terminal part # 60012931 in AFL Tray 21, along with wire seal part # 60994015 in AFL Tray 21 and connect it to one end of the wire. Disconnect the X400 connector and remove the rubber cavity plug in pin position 4 and discard. Install the terminated lead that was just made into the X400 connector pin 4. Run the wire up to the CHMSL for the cap or topper and connect. The ground for the cap or topper CHMSL will need to be made to an appropriate ground.

For vehicles built WITHOUT Under Rail Bed Lighting Option:

Trucks not equipped with the under rail bed lighting option will have a dummy X400 female connector, which will be removed and discarded. The female side of the X400 connector is not available separately, but can be obtained by ordering the under rail bed lighting harness GM part number 23327843. The harness will come with terminals/wiring in pin positions 1 and 6. Remove the wiring and terminal from pin location 1 and discard. Move the rubber cavity plug from pin position 4 and reinstall it into pin position 1. Obtain an appropriate length of 18 ga wire to run from the X400 up to the CHMSL wiring for the cap or topper. Use terminal part # 60012931 in AFL Tray 21, along with wire seal part # 60994015 in AFL Tray 21 and connect it to one end of the wire. Install the terminated lead that was just made into the X400 connector pin location 4. Pin 6 is a ground circuit that is used for the under rail bed lighting and it can also be used to ground the CHMSL for the cap or topper if the wire gauge size in the connector is of the proper size for the CHMSL in the cap or topper. If the wire gauge size is too small, any of the following can be done:

Make a second wire as described above. Then, remove the wiring from pin 6 and discard. Install the new terminated wire in position 6 for the ground and run it up to the CHMSL for the cap or topper and connect.

Remove the wire and terminal from pin 6 and install a rubber cavity plug.

Cut the wire for terminal 6, leaving a couple inches of wire, and seal the end of the wire.

Note: The terminal removal tool for the female side of the X400 connector is J-38125-212.

You can get the terminals from your dealer or an online electronics place like Mouser Electronics.

jim larson · June 17, 2020

Thanks this is really helpful. I call the service department and they indicated they had nothing; but I could take the car in @ accessories rate $'s and they could wire it. And I have bought my last 5 trucks and 2 cars from them. I will be mentioning that to my salesman who is the owners son.

davester · June 18, 2020

There might be info on gmupfitter.com about this (and it appears to be back up now).

newdude · June 18, 2020

20 hours ago, jim larson said:

Thanks this is really helpful. I call the service department and they indicated they had nothing; but I could take the car in @ accessories rate $'s and they could wire it. And I have bought my last 5 trucks and 2 cars from them. I will be mentioning that to my salesman who is the owners son.

Go see them with this document # #PIT5314C: CHMSL Wiring for Aftermarket Bed Cap Topper - (Jan 7, 2019)

Its the document they can pull up that has the info I already posted here for you. They "had nothing" because they "didn't look".

jim larson · June 18, 2020

how do you find that, I am not familiar with the process

jim larson · June 19, 2020

well I pull the light housing today. not sure where the X400 connector is. I thought it would be the c connector to the bulb in the light housing. i am not sure that is the connector as I don't see a dummy spot. There are 4 wires there. one of those spots doesn't seem to have any power. my guess is that would be the ground, is that so? So is there one wire that is dedicated to the brake light only? I can't seem to determine which one to use so the brake light doesn't blink. I will take some photos and post. I think the black is the ground. Don't know what the red, green, and brown wire do. Or where the x400 connector is located if this is not it.

Jim larson1 · June 19, 2020

Confused by instructions, is the X400 connector in the light housing. If this is it my has 4. Wires, a black I think and a red, green and brown. Here is a photo hopefully.