A direct-through mod is a very useful tone shaping tool. It will help you make your Telecaster tone brighter and more dynamic when you will need that. It's based on a DPDT switch (push-pull), used to connect pickups directly to the output, by omitting pots.
Diagram:
Previously, I made this mod in a Stratocaster. I used a toggle SW. For Telecaster I recommend a push-pull pot. These guitars don't have much place for toggles - if you don't want to drill.
How it works?
As you can see, the pots, the pickup selector and their connections are common, typical for Tele. When the push-pull knob will be down, everything will be working in the standard way. The direct-through mod will be off.
When you will pull the knob up, the switch will disconnect pots from the hot path, and signal will go directly to the jack, only by pickup selector.
The 250K Telecaster control pots make the tone quite warm, well balanced. When they are disconnected from the wiring hot path, the guitar tone becomes much brighter and more dynamic. You can make it by one click of the switch. It's a great modification for aggressive solos or crispy rhythm riffs.
