This video explains the process of making custom extension cords and socket light sets for elaborate Christmas displays.
Below are some vendor links for SPT 1, SPT 2, socket wire, vampire plugs, and vampire sockets. I have purchased product from all and would recommend each.
http://www.creativedisplays.com/
https://thechristmaslightemporium.com/
http://www.allthingschristmasandmore....
http://www.christmaslightshow.com/
https://www.homedepot.com/s/slide%252...
https://www.menards.com/main/search.h...