Telephone Wiring Diagram - Ask-The-Electrician You will have a wide variety of telephone jacks to choose from but the wiring for a single line phone service will be standard. Keep in mind that the colors of the telephone wiring in your home will be typically one of two types or insulation colors. Older telephone wiring was a basic Cat-3, 4 conductor or 2-pairs with red, green, black, yellow.[PDF] Lets go over the basics of telephone wiring. Lets go over the basics of telephone wiring. Once you understand the basics, troubleshooting becomes a breeze. It may be time consuming, but a breeze. And at $40 or more for a half hour's service from the telephone repair guy, the wind will be at your back!! The really basic basics of telephone wiring..