CobraCmdr

Eureka! I got the crazy thing working! Mad props 15HDriver for the tips and info. The factory wire was left nice and tucked away, wrapped in black tape, inside of the connector in the UBEC as you mentioned and we hoped hadn't been cut off LOL I took pics as I made my way down to the wire inside the UBEC to help explain what I found and did. (one thing to keep in mind, I didn't disconnect the battery...some people on other sites said to do so, others didn't.) Once I was able to get the UBEC up and partly out of the way, I found connector X3 and saw the wire from the sport bar brake light going into it. I opened up the connector to expose the wires: Found the factory wire all nice and taped up! Next thing I did was to carefully pull the black tape off, making sure not to damage the wire Then, turning the connector X3 around, I found the sport bar brake light wire. I marked the port, just in case I forgot which one it was in. Then, I turned the connector back around and removed the blue clip to expose the latches that keep each of the wires in place. This part was a bit of a pain as the clip is pretty thin, and I didn't want it to break, so it just took some time to ease out of the connector. Once the clip was off, I used a probe tool to push down the latch that held the wire for the sport bar brake light and then slowly pulled the wire out. After that, I inserted the factory wire into the port where the sport bar brake light wire was and then reassembled everything, making sure everything was free of debris and snug. I used black tape to wrap the sport bar connector and just taped it off in case I, or someone else ever wants to reinstall the sport bar again kweable, it's totally doable yourself if you have some patience and a few tools. Really, the only part that was a bit crazy was taking off the blue clip on the X3 connector. Hope the pics helped! EDIT: Worth noting that when starting the truck after the EBEC is disconnected/reconnected, there were several things that popped up on the info center: outside temp alert (noticed the displayed temp on the nav screen showed 32F, when it is was actually 73F here today) and something about Driver 2. Both of these alerts cleared and the temp corrected itself after about 10 mins of driving. I'm guessing stuff needed to resync/calibrate after the EBEC was disconnected for so long. Anyways, just a headsup

I may try this between now and my next service appt. on the 30th I printed out the section that mentioned the stuff about the UBEC and took it with me to the dealer for my recall appt today. The service guys seemed to understand what needed to be done, but didn't want to make me wait. But then they mentioned something about "if the harness going to the CHMSL isn't right" and "we can always just run a new wire to it"... That got me a bit nervous. Don't want them tearing up the truck running new wire if everything they need to do is right there xD I'll update with pics of the wires, removed UBEC, etc next time I get a chance to work on it. I'm just hoping factory didn't end up cutting the original wires...

After reading this, I think I might have been looking for the wrong thing around the UBEC yesterday. So rather than the harness connector, I should be looking for that single (purple) wire that was removed in the UBEC itself, right? I was looking at this connector before:

Will do! Apparently my dealer's service team has a great rep from the reviews I'm reading. I'll put 'em to the test with this one! LOL I found out some more info thanks to 15HDriver's post, see below This info was perfect 15HDriver! I had a hard time picturing where the harness would be in/near the UBEC, so thanks to some keywords from the info you posted, I was able to search online a bit more and found another post about this exact issue where a Silverado owner removed their sport bar and had the same problem: http://www.justanswer.com/chevy/9odun-chevrolet-silverado-1500-classic-lt-removed-factory.html The tech's responses gave me even more keywords to search with and lo-and-behold I found a diagrammed installation for the sport bar on an eBay seller's storefront: http://www.ebay.com/itm/2016-GMC-Sierra-Bed-Mounted-Sport-Bar-23387669-Genuine-OEM-GM-/112026710099 About half way down the install diagram, the UEC is shown and they have a diagram of how to take it out and also where the harness should be. I decided to take a stab at it and was able to get as far as removing the UEC part way and found what I think the factory harness to sport bar harness was. I just couldn't find the original terminal...or I wasn't reading the instructions right. I saw a similar connector deeper down in the bay, but I wasn't comfortable just pulling plugs all over the place LOL. I'd post pics, but it was getting dark out (don't really have a work area at my place where I can fit my truck atm LOL) I think I might have missed this step: Locate the CHMSL circuit in cavity M6 of UEC connector X3. It will be the grey, rear, outboard connector. Remove the terminal from cavity M6. It will be a VT/GY wire. Replace it with the smaller of the two terminals, with the shorter wire length on the new accessory harness. Anyways, I'm gonna try again tomorrow and will post pics of what I find. Worst comes to worst, I can explain in detail what I've tried and searched for to my dealer service crew

Finally found a post about this! Newbie here, I'm in the same boat as the OP As I was taking out the sport bar, I had a feeling the third brake light wouldn't work, but was hoping a relay or something else would activate the cab brake light if it didn't detect the sport bar brake light (wishful thinking...LOL) I tried changing bulbs on the cab brake light, even rotated the bulb (not sure if it matters)...nothing I checked the CHMSL fuse to make sure it was good, or even there. It was there and good. I noticed the wiring for the harness for the sport bar brake light was the same as the wiring for the harness on the cab brake light (at least the color coding was the same), so I decided to follow the sport bar harness wiring underneath to see where it led. It ended up at a junction where the factory had spliced into/onto the main wiring under the truck. Maybe the cab wiring is not connected here? I dunno. At this point, I stopped tinkering. Didn't want to open anything up that might void warranties (truck's only a few months old LOL) I made service appt with my dealer and am going to tell them what I've figured out so far...hoping it will help lead to a quick fix before I get pulled over by a quota happy cop! xD I'll update here if the dealer finds a fix.