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Discussion Starter · #1 · (Edited)
Greetings all!

Recently I picked up a topper off of craigslist for a great deal, but in doing some research to wire in the dome/third brake light found there wasn't a clear tutorial on how to do this. Specifically if you have a dual function brake light bulb and only want it to be a brake light. I am not a professional, but I work on all my own vehicles and wanted to really "nerd out" on the proper way to do this before cutting into my vehicles wiring harness. This is very pic heavy with OEM wiring diagrams/Vendor diagrams and a step by step tutorial for those wanting to try it for the first time.

First a few disclaimers: Wiring the dome the dome light and the CHMSL (Center High Mount Stop Light) are very easy tasks you can do. One of the first problems you'll run into is because of your dual function tail lights you cant just wire it in like a normal topper. Well, you can but then the topper will blink with the signal instead of acting like a brake light. The obstacle for me was finding out which way I wanted to do it and the proper way to do it, as my truck is a 2020 Chevy Colorado Duramax and the thought of splicing willy nilly made me uneasy. If you are a professional or a trained technician, this probably isn't the guide for you. I just wanted to show my work and the way I came to my conclusion.

1.Pre-Planning:
Attached is the .PDF resource that the local Leer dealer gave me to how they wire them up. This was good and bad, because the wire they tap into was up under the drivers part of the dash. I wasn't really interested in running a wire from the topper to the dash. (Lots of panel removing and routing wire) not to say you couldn't but this made me reconsider.

The local dealer also included these instructions:

Our canopy installer said that the red/white wire are for the third
brake light. Black is ground and Red positive (as normal) he said to
ground the canopy lights to the chassis. If you have a 7 way plug for
towing, you can splice into that with either a scotch lock or heat
shrink butt connector for power to the dome light. Any questions, please
feel free to call.

(Very nice people, great resource to reach out to if you have trouble is your local canopy dealer)

I also went to my local auto parts store and printed out the wiring diagrams for our trucks to look over to help me make the best decision. This (although very tedious) was helpful in a way to help trace back what feedback I was getting on what wires to tap into. I've attached all of these to the post as well.

2. Supplies:

I gathered some T-Taps from my local auto parts store.
Heat shrink and heat shrink butt connectors
18-22 gauge wire that I had lying around in the garage. (tried to color match as much as possible).
Multimeter
9V battery
Scotch 3m electrical tape Super 33 (Trust me)
Plastic wire loom
Logic module (ATC AT-LC-8N) is the one I used from SiraWeb. I highly recommend it. It's very durable and straightforward, ships to your door about a week but well worth it IMO.
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3. Testing:

First depending on how you got your canopy (used most likely) you'll want to test everything and make sure it works. To do this, grab a 9v battery and attach + to + and - to - of the dome light. Once tested you'll likely have this junction box that is fused on the side of your topper with some wires coming out. You can OHM check the fuses at this point also, just to make sure there's nothing screwy going on. Mine just had the wires cut so I wanted to make sure of everything. So I went through and tested them and then labeled which was the dome vs. CHMSL. You can use the multimeter as well to find a good ground location if you choose to route it a different way.
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3. Begin the Operation:

Next, you'll want to remove your driver side tail light assembly. This is very straight forward. Take the two small torx bolts out of the side and while applying cautious pressure negotiate the housing from the assembly. (Everything is plastic be gentle). With this removed (you can just unhook the bulbs to not leave it dangling) and your wires tested you'll want to figure out how you'll be routing your wires and where you want to attach your ground. I suggest the ground point I used as it's well protected and works well for both the dome light and the brake light ground. I started with the dome light as you don't have to worry about messing with the logic module yet. I routed everything through the nearest hole in the bed. I actually popped the rubber plug out and took some shears and took a quarter out of it, fed the wires through and then silicone it back up. I also used weather proof connectors for everything I did, the ground that I ran I actually went to the hardware store and grabbed a longer bolt in the second picture to make the best connection. I matched the threads and just added a second nut to keep the ground nice and tight. You can also ground the logic module here as well. I just ran the wire straight down from inside the taillight housing.

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4. Continuing the operation:

Then, using the logic module it's very straight forward. Connect the colors to the appropriate labels and then route the wires as you see fit. I ended up splicing into the 7 way trailer connector as suggested by the Leer dealer. It was a lot easier and it required to removal of any panels or routing of wires. You can achieve this by getting under the rear bumped or popping the 7 way trailing harness out (if equipped). Either way works fine and I actually found it easier to cut the stock wire loom back a ways and work underneath the truck so you can attach your T-Taps back a ways to repair or replace should anything happen. I must remind you, PLEASE HEAT SHRINK EVERYTHING. The T-Taps shown are not weatherproof so I added heat shrink at every turn. A little patience in this area will pay dividends in not having any wiring issues in the future. The purpose of the logic module is to isolate turn signal flashes and only produce brake light flashes, so when you connect it you will wire it up directly to your corresponding wires of the trailer plug.


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Once everything is attached, re-loom and route the wires in their final resting place. I chose to mount the module up under the driver side tail lamp using zip ties. I also re-loomed the entire wiring for the topper using plastic loom and electrical tape blending into the existing loom. Reassemble and grab your nearest brick to put on the brake pedal to see how if your handy work has paid off.

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Thank you all, I hope this helped in any way! I will attached the rest of the diagrams I studied and overthought every step of the way lol!
 

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2018 Kinetic Blue Ex-Cab ZR2 V6
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Seriously, how did this thread fall through the cracks? I know several folks have wondered about wiring. I am certainly one of them. Nice writeup!

I'll add it to the list of crap I need to do.
 

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2016 Colorado WT, crew cab long bed
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I used this video to wire my third brake light without having to buy a logic box module. It’s more involved but just another way of doing it. The dome light can just be wired in to that orange wire or ran to the battery alongside the third brake wire if you are going this route.


Sent from my iPhone using Tapatalk
 

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2016 Colorado CCLB Z71 diesel Rainforest Green
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Or you can do what I did...


Essentially, the same thing, but no cutting and splicing...all plug-n-play...costs more, but no hacked wiring.
 

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I didn't know about the leer harness when I did mine. I did essentially the same thing, but purchased a splitter harness that goes between the 7 pin connector and the oem cable so that I didn't have to splice anything.

 

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I didn't know about the leer harness when I did mine. I did essentially the same thing, but purchased a splitter harness that goes between the 7 pin connector and the oem cable so that I didn't have to splice anything.

We're you able to wire an interior light inside the canopy as well as the brake light with this? Thanks
 

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Oh I thought the brown wire was the one needed for the brake light?
No, the way the brake lights on trailers with the 4 pin connectors work is it's just the turn signal bulbs both on solid. So you only really need the left and right turn signal and ground wires from the 4 pin harness. You'll have to use a logic box so that the brake light only comes on when both turn signals get power. Otherwise it will flash when you have the turn signals on.

I used the unused brown wire to run power up. If you get the splitter I posted, use electrical tape over the shrink wrap that comes with it. Mine just corroded apart after probably a year because water got in it.
 

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No, the way the brake lights on trailers with the 4 pin connectors work is it's just the turn signal bulbs both on solid. So you only really need the left and right turn signal and ground wires from the 4 pin harness. You'll have to use a logic box so that the brake light only comes on when both turn signals get power. Otherwise it will flash when you have the turn signals on.

I used the unused brown wire to run power up. If you get the splitter I posted, use electrical tape over the shrink wrap that comes with it. Mine just corroded apart after probably a year because water got in it.
No, the way the brake lights on trailers with the 4 pin connectors work is it's just the turn signal bulbs both on solid. So you only really need the left and right turn signal and ground wires from the 4 pin harness. You'll have to use a logic box so that the brake light only comes on when both turn signals get power. Otherwise it will flash when you have the turn signals on.

I used the unused brown wire to run power up. If you get the splitter I posted, use electrical tape over the shrink wrap that comes with it. Mine just corroded apart after probably a year because water got in it.
Thanks for the info. I went ahead and bought the leer harness today. Going to install it tomorrow.
 

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Finished the install everything went smooth and works with no flash when using the turn signal. Interior light works and brake light on back of canopy. Plug and play super easy no cutting into wiring harness etc. Do not install the white 4 pin connector before you run the wires thru the hole in the truck bed. It won't fit thru the hole so I had to use a brad nail and disconnect the molex connector pins run the wire. Used a coat hanger shoved it down taped the 4 wires and pulled thru. Leer 7 way 300100 is the way to go! Only bad part is the price!
 
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