Regarding a 16 function 150 mini light parellel string with 4 wires from adapter; there are three colored bulbs one (blue) does not light. The functions work well and I changed the 2 fuses in the plug (out of desperation as I knew both fuses had to be working for any lights to work). I am getting ready to attempt to open the adapter (not easy to do as it has a tiny triangle to fit the head of the screw into); any ideas? Set is new used this Xmas season. Thanks to any who has any ideas.

 

and you've plugged the "not working" bulbs into a different area of the string and they light? Any cuts/nicks/breaks in the wire. (should be easy to diagnose with a multimeter)