WEIRD LEFT INDICATOR FAILURE

[xIIPHOENIXIIx]

So couple days ago my left rear turn/brake started acting up. I get the left rear indicator failure message. The bulbs are fine, I checked the fuse and its was good too. I went ahead and got a new fuse and bulbs and installed them, yet nothing. With a tester I tested the power coming from the BCM thinking it went out but no power comes out. I tested the fuse also and it lights up/flashes when the turn signal is on or step on the brake. I checked the entire harness and there were no signs of cuts. Here is the weird part this shit will work when it wants. It can be fine for two days and then the next day it wont work and will last until it decides to work. So II was thinking it was a relay when it gets hot it wont work. As it cools down it will start working again until it heats up or bullshit like that. That's my only solution as of right now. Does anyone know what relay it would be? OR WTF is could be? The right side works fine all the time. I shared a pic of the wiring diagram to give a better example of what I'm saying. 

 

THANKS FOR ANY HELP!!!

[BigBadSierra]

It may be a bad socket connector on the end of the harness Had an issue like that on a 05 Colorado. Had to replace them..

[xIIPHOENIXIIx]

That's what I thought too, so I went ahead a got two new taillight harness & the motherboard behind the bumper where the plug in.

[RevolutionAnarchy713]

Where did you find the fuses at?

[Donstar]

The first thing that came to my mind was a faulty ground.  It sounds to me you have already gone above and beyond the steps needed for a DIY solution.  Go to a gm service facility that you trust and get it checked out.  You  may be missing something simple and obvious to someone else who is able to physically see your vehicle.

A good example of my advice recently applied to me personally.  Last week I was out in my brand new Winnebago TT and  I could not get the park's cable to work for my TV.  I asked for help on a Winnebago forum and traced all of the wiring.  I even phoned an RV service department.  Two days later I explained my problem to the park owner who was very knowledgeable on the topic.  The first words out of his mouth were, "you need a cable box."   This sounds obvious now, but it was totally out of my realm of consideration that you'd need a home-style cable box at an RV hookup!  Nobody on my RV forum or at the RV dealership even hinted at a cable box!

[David Schneider]

Yeah dude I'm having the same problem with my truck but now my tail light went out all together with two brand new bulbs so something in the wiring or my sockets. Cuz when I replace my top tail light the sockets were so corroded I couldn't get the light bulbs out but now left turn signal failure. Is on all the time.  So it's got to be somewhere in The wiring.  Or bad relay some where

[OneFatCat]

I have been battling this issue and found that the problem is with the metal contacts on the bulb itself. They lose contact over time. Take the bulb out and bend the two natal contacts out slightly and then reinsert. I hope this works for you too.