Headphone Repair - iFixit
How to wire a telephone - Quora
Vintage 1/4 (6.35mm) Phone Jack Plug by Winston
What is a TRS Cable? – Mission Engineering
Modular connector - Wikiwand
How 1/4 inch Audio Cables Work
TRS connector - Wikipedia, the free encyclopedia
4 Ways to Check a Phone Line - wikiHow
LocoNet Throttle Network - DCCWiki