LED strip light not powering up after installation.

Hello!
I bought 16 ft of 12V Flexible LED Strip Lights rated at 4.4 watts/ft and a 12V, 72W Max, power supply. Out of the box, they worked fine but after cutting and soldering the light sections I noticed some occasional flickering and when I finally added the last two light sections, it will power on for half a secund and then go back of again.
I used gauge 20 Twisted Bell Wire to connect between the light sections. I'm thinking that perhaps the added resistance of wire length, of about 15 feet total, might have impacted the system but I'm not sure. Can someone please help me figure it out?

I'm attaching a diagram of my setup and a picture of the project before adding the last two light sections (at that point it was powering on but noticed some occasional flickering)

 

Steve, thanks for you reply, I should have researched more before starting this project, unfortunately some of the bell wires are running behind the kitchen backsplash and I don't see a viable way of replacing them.

Question: Having the following configuration in series: POWER SUPPLY ---- LIGHT SECTION 1 ---- LIGHT SECTION 2 ---- LIGHT SECTION 3, if there is a short in section 3, could it cause sections 1 and 2 not to turn on?

Any tips that could help me troubleshoot and pinpoint the issue is highly appreciated. Thanks!

 

Thanks! I'll try that and report back.

 

IT WORKED!! I found where the issue was by testing for continuity on all the sections and it was indeed on the very last section, fixed it and now all the sections light up.
But, now there is flickering on the last section. Could it be still a faulty connection? I plan to replace and re-solder that section and report back.

 

Hey!! Everything is working perfect now. I'm attaching a picture of the final result, still needs some painting but the kitchen project is finally done and thanks to you for all the tips.
The flickering was due to bad soldering.

If I could give some advice to newbies out there:
1. Learn to solder and practice before starting your project. It's important to warm up the wires before soldering otherwise you could get faulty connections.
2. For LED light strings do not use clip-on connectors/extenders, solder instead (avoid headaches)
3. Use the right gauge wires and as recommended by Steve, use stranded wire
4. When problems arise don't panic, get a multimeter and test. Thanks Keith!