Driver side brake light on trailer not working - problem in the truck

[BoxMN]

2005 Trailblazer lights work fine on the truck, Hook up a trailer and everything works except the driver side brake light. 

Hook up trailer to any other truck and all lights work. I tested the 7 to 4 pin plug and it is ot the plug, even tried a new one. So I think the truck 7 pin connector might be the issue. I did not try to clean it yet. This is the factory connector/female part, and I haven't crawled under there yet to look - is this an easy "unplug old part, plug in new part" type deal? Or would it involved a bunch of splicing?

Thanks for any advice!

[Macgyver55]

Is it just the brake light or does the left signal also not work on the trailer? If not working, fuse #51 should be checked in the under hood fuse box.

[brian6715]

Yeah that is a fuse, easy to find under the hood. Had the same issue with my Chevy and my Dad's, turned out we had a trailer that had a short that would blow that fuse. 

[BoxMN]

The left signal works fine. It is just the brake light that doesn't. I checked fuses under the rear seat, but not under the hood. Will check for that fuse.

Do you mean if only the brake light, then it is the fuse? Or if BOTH the brake and left signal, ten a fuse? Thanks!

[Jeremy airjer W]

if both the brake and turn are not working than the fuse would be the suspect.
 

since the right side turn signal works than it is safe to say that 7 way and the wiring to the seven way are good. Since the turn signal and the brake use the same wiring.

 

I am all in on the turn signal flasher module. Pin D will be a dark green wire. If there is no power there with the brake depressed and there is power on the yellow wire, Pin C, than  it is bad. The yellow wire is the left turn/brake.

[BoxMN]

Thanks guys, the fuses look good, and it seems like it likely is the module. I think that is my next step. I will post back after I get one and plug it in.

After reading Jers notes, I read more and it seems like a common thing on those GMs, at least the trailvoy models. I believe this is the part I need - funny how the name of this part can be called several different things:

ACDelco 15231201 GM Original Equipment Hazard Warning and Turn Signal Flasher

[BoxMN]

So I finally got the part today, $34 from Amazon, it was $40 from my nephew who usually gets me pretty good prices.

It is now working again! It took me a bit longer (30 minutes)  than it should have, as I dropped the trim under the steering wheel instead of just the bottom black bracket. The part itself resides in the black bracket, so I would not have had to take more than 2 screws out, and doing it again it would take about 5-10 minutes. 

Thanks Jer for nailing the issue, again!  And thanks to all as I now have a better understanding of the turn signal operation and fuses.

Next is water pump in my k1500...

[Jeremy airjer W]

Next is water pump in my k1500

It could be worse. You could have spent 5 hours on your knees buried in the wheel wells of a 2500HD drilling out broken exhaust manifold bolts an then spend another couple hours sitting in the engine bay replacing the knock sensors..... Just sayin

[delcecchi]

Depends on what you get per hour how painful it is...... 

 

 

[BoxMN]

I wouldn't even know where to look for a "knock sensor"

[delcecchi]

I wouldn't even know where to look for a "knock sensor"

Probably because they are painted camo so you can't see them.