This is my first post so I'm not sure how this all works haha, but I have a 2005 Suburban 1500 LS. So a while back, my third brake light went out. Naturally, I purchased a new one, however the new one didn't work. I used a multimeter and confirmed that there was power going through to the light and I tried using some dielectric grease, but the light still would not work. I returned the light and bought another, only to find that didn't work either. I decided to give it one more try and the third one I bought worked finally. But something odd I noticed was that even after installing the new brake light, my left turn signal still flashed rapidly (as if the light were still out). I decided it wasn't a terribly big deal and just went about my day ignoring the differing tempos in my turn signals. Overtime, however, the right side began also flashing rapidly. This progressed to the turn signals being on solid. I did some light research and found out the flasher from my era of truck had a tendency to go out. So I bought a new flasher, and the problem was unchanged. I did some more research to find out that GM had updated this part so I bought their updated flasher, and nothing changed. I'm currently at a state where my turn signals only work when the headlights are off (they still flash rapidly) and when the headlights are on, the turn signals are both on solid. I have attempted changing out the flashers and the bulbs so I would assume I have a wiring issue but I wanted to see if anyone here has had a similar issue and could help me out. Thanks.

 

Check your grounds

 

Can't help with this, but welcome to the world of GM !!!

 

I'm going to be honest lol, I don't know a ton about electrical things. I saw this same tip when researching and I don't exactly know how to do that.

 

Most of the metal in your truck: the frame, engine block, body etc... is connected to the negative terminal of your battery. That way, manufacturers don't need to run a dedicated negative wire to all the electrical bits. The whole thing just acts as a negative terminal. The electrical system in your truck has hundreds of places where the wiring harness or an accessory it is connected to this so called "chassis ground". For example, you will see them behind every light cluster, the stereo, near sensors etc. All these things rely on these ground connections in order to make a complete circuit and work properly. Everything needs a solid connection to positive and negative right?

When there are a bunch of things close together, like a brake light, tail light, turn signal, etc. then they will sometimes share a ground connection, which sounds a bit like your situation. The ground connection is usually just a ring terminal with a bolt through it. Sometimes the bolt becomes loose or corroded or whatever, and you end up with weird or intermittent electrical gremlins, because the circuit "goes open".

The rapid flashing is a sign that a circuit has gone open, such as when a bulb burns out OR there's a bad connection.

Simply testing for 12V on a bulb socket is a not a guarantee that the lamp will work. It needs 12V AND ground.

https://www.thedashcamstore.com/how-...-ground-point/