Etrailer.com and EasternMarine.com are two websites that provide trailer brake wiring diagrams. Each site offers a detailed wiring diagram for a typical brake controller installation, and Etrailer.com offers several additional trailer wiring diagrams.
Etrailer.com provides a diagram for a four-wire trailer brake installation and identifies the purpose for each wire color. Instructions on how to attach each wire connection are also available. This site also offers diagrams for trailer wiring connectors with up to seven pins, as well as a chart that outlines trailer wiring color codes. EasternMarine.com offers a wiring diagram for a commonly used electronic brake control and provides special instructions for certain vehicles.