Just wired lights they are not working.

How? What can possibly fail on them? I just bought some to add some amber leds to the cup holders. I can tell you damn near anything I solder will most likely eventually fail too.

 

They make a poor mechanical connection. Movement and corrosion lead to poor connections, potentially wire breakage.

The blade is punching through the insulation and contacting the stranded conductors. In a vehicle that is constantly vibrating, the edges will cause the strands to break, ultimately leaving you with a "fuse" at the contact point.

There is a reason that factory connections are crimped and never "quick tap"

Proper soldering will not fail.
Proper soldering includes having a solid mechanical connection before applying the solder, not "wicking" the solder up inside the insulation, and providing proper strain relief so there is no flexing force applied to the solid portions of the joint.
Proper soldering also includes proper insulation and waterproofing if the wire is going to be in a damp location. Ignore waterproofing and water will wick through the entire conductor, corroding the wire, and leading to a break at a point subject to regular flexing.

 

I'm gonna return them. Thanks. I definitely don't want to have to trouble shoot my work down the road. I need to tighten up my soldering skills.

 

Ya... I keep them available, but I only use them for testing or temporary connections. Once I'm satisfied with how everything is working, I remove them and make a proper splice.