Factory Trailer Wiring Problem
 

I have a 2004 Chev Suburban 1500 4wd Z71. I have recently found out that I am not receiving a left side brake signal to the factory installed 7-pin. Everything works on the truck and at the 7-pin except the left side brake. Even the left turn signal works. Checked EVERY colored fuse inside and under hood. Any one have any ideas what the issue could be??

Welcome to the forum...
have you check for the signal at the 7 pin socket?

Might want to probe the wires at the back side of the connector, perhaps you have a defective socket...

I did. 7-pin has no power at the left side terminal when brake is depressed. I even took the plug out of the factory 7-pin and tested it. There is no brake signal coming to it when brake is depressed. Only when the left turn signal is on. It's definantly a problem coming from the front somewhere.

Does the right side turn get the brake lamp signal?

Have you checked all fuses? Note that there are 4 fuses for the stop and 2 for the signals ( see illustration below)

LT TRLR ST/TRN Fuse
10A
Trailer Wiring

fuses
 

when my trailer's left turn went out, it was a fuse. I was like what the heck? because the lights on the truck still worked... I didn't know they seperated the trailer lights...

Was this ever resolved? I'm having the exact same issue.

I have been researching like crazy and havent found a solution yet>
2012 Tahoe PPV-I recently set it up for towing. Purchased a direct plug and play 7-pin trailer connector. First time I turned on 4 ways, the right signal did not work.
Found the fuse blown...which was odd because this circuit has never been used before. Changed the fuse and it worked. Over the past couple of weeks, the fuse keeps blowing. I disconnected every thing I installed, replaced the fuse and tested with a test light...al good. Tested the new plug and play harness for shorts...all good. Reconnected and plugged in a 7-pin tester. all good. Thought it was good to go. Blew the fuse again. Trailer is brand new. Fuse is blowing without trailer connected.
My next step is to have someone probe the fuse while I crawl underneath and wiggle the harness around.
Option is to tap into right side signal light feed and run a jumper to the trailer harness and cut the wire back to the fuse box. Of course I will put a fuse on this line. Trailer lights are all LED so overloading is not an issue.
Current stable:
2005 Express 3500
2011 Traverse
2012 Tahoe PPV

Solution!
 

So I was having the exact same issue as the OP. Both turn signals were working on the trailer, but the right brake light wasnt working. After hours of research, I saw a thread where someone was having a similar issue and it ended up being a faulty turn signal flasher. I took mine out (located to the right of the fuse panel in the cab) cleaned the connections, and it fixed the problem. Hope this helps anyone looking for a solution, and hopefully saves people some time scouring the internet.