Driver side Turn signal on front and back does not work?

Tiny
FLYINGRHINO
  • MEMBER
  • 2008 GMC SIERRA
  • 5.3L
  • V8
  • 4WD
  • AUTOMATIC
  • 202,000 MILES
All of the lights work on both the front and back head/taillights. However, whenever I turn on hazard or left turn signal, none of them work on the left side.

I get good voltage directly from the turn signal switch that is connected to the steering wheel. Tan wire goes to right has good voltage and can see it open and closing same with the green on the left.

I had to cut open the tape coming from the steering wheel to trace where the wires are going and they are connected to the top side of GM24242480 Module assembly transfer case shift control, or at least there is some other type of module behind it that it plugs into.

So, going from the turn signal switch to the back of the TCM the voltage is working as it should and somewhere after is where I'm losing my signal.

I can't figure out if I have a bad ground somewhere in between, but as I said before, everything else works on the headlight.

I honestly have no idea where the wire goes after the TCM as I don't have very good access behind it.

I have the Haynes repair manual for my truck, so I have all of the wiring diagrams but can't figure out where my signal is actually dropping. I'm trying not to have to replace the TCM or whatever is behind it due to one wire.

This happened when I was in the process of installing new headlights and switchbacks. It had worked at the beginning and then all of the blinkers on the front and back went out and never came back. One last thing is those lights that are being used for blinkers do come on in the front on the left as well, they just never blink.

Finally, there is an aftermarket mirror on the driver's side that has a turn signal installed in it. The passenger side only has the standard mirror. I haven't tried to diagnose if that is the problem. However, there were some loose wires that I repaired because every time that I used the electric mirror control to the left it would pop a fuse.
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Monday, September 26th, 2022 AT 7:42 PM

5 Replies

Tiny
KEN L
  • ADMIN
The aftermarket mirror could be the issue if they tried to wire it in, so, I would look at that. Also, what do you mean by I installed switchbacks? Also, where is the replacement bulb OEM? If you follow the yellow wire that powers the left side turn signal you will see the only thing that is supplying power is the BCM. I would check the connection between the BCM and the turn signal bulbs and if okay, replace the BCM. here are the turn signal wiring diagrams so others that see this post can understand what we are talking about and how to replace the BCM and its location as well.

https://www.2carpros.com/articles/how-to-check-wiring

You can get a preprogrammed BCM if you search Google or Ebay. Check out the images (below). Let us know what happens and please upload pictures or videos of the problem.
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Tuesday, September 27th, 2022 AT 10:31 AM
Tiny
FLYINGRHINO
  • MEMBER
I was in the process of installing switchback bulbs as well as new headlights when all of this started to happen. I don't have the OEM headlamp or bulbs as I bought this truck used 2 weeks ago. I bought new headlamps for the truck with an LED running light strip and when I got to the left side, while the wiring harness was correct, it was tied into sockets that didn't match the truck and didn't have a good seal, so I replaced them.

I ended up taking the switchbacks out and installing standard turn signal bulbs, so I wasn't dealing with rapid flash while trying to solve this issue. However, I decided to put them back in last night to see what they would do and on the left side they only lit up amber and would never, I'm guessing, would supply enough power to make the lights turn white, unless it simply means I have some wires crossed somewhere?

I will check the wiring from the mirror and see where that leads.

Could my wiring be messed up at the headlamp harness because I'm getting full power to the yellow wire at the headlamp? Also, I did notice last night after I posted my question that I'm also not getting a brake light on the left side either but the bulb isn't blown. I'll post a video of the issue later.
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Tuesday, September 27th, 2022 AT 11:17 AM
Tiny
FLYINGRHINO
  • MEMBER
Update: I found the harness that goes to the headlamp, and I had it unplugged, and the rear began to work again. Signal and everything. Once I plugged it back in and blew LT Stop TRN fuse.

Photo is of the harness I had unplugged. This harness feeds into the under-hood fuse box then back out into the cab.

Would this be a bad ground issue or a 12v wire touching metal somewhere?
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Tuesday, September 27th, 2022 AT 3:25 PM
Tiny
FLYINGRHINO
  • MEMBER
Got it fixed. Turns out it wasn't anything with the truck but my faulty wiring on the parking light on the headlamp. Thanks for your help.
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Tuesday, September 27th, 2022 AT 4:08 PM
Tiny
KEN L
  • ADMIN
Thanks for getting back to us. Nice work, we are here to help, please use 2CarPros anytime.
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Thursday, September 29th, 2022 AT 12:51 PM

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