What wire does the tractor send power to the trailer taillights?

In a standard 7-pin trailer connector configuration, which is commonly used in North America, the wire that the tractor sends power to for the trailer taillights is typically the brown wire. This wire is labeled as the "Tail/Marker Light" or "Running Lights" wire. It supplies power to the taillights and running lights on the trailer, allowing them to illuminate when the tractor's headlights are turned on. The brown wire is one of the key connections for lighting on the trailer.

The trailer connector is designed to establish electrical connections between the tractor and the trailer, allowing various signals and power to be transmitted for lighting, braking, and other functions. The connector has multiple pins or terminals, each serving a specific purpose.

The 7 pins in a standard North American trailer connector are typically assigned as follows:

Left Turn and Brake Lights

Ground

Tail/Marker Lights (Running Lights)

Right Turn and Brake Lights

Electric Brake Control

Backup Lights (if applicable)

12V Auxiliary Power

It's important to note that the color coding and pin assignments might vary depending on regional standards and the specific wiring setup of the tractor-trailer combination. If you are in a different region or using a different connector standard, the wire colors and functions could be different. Always refer to the documentation or labels on the connector itself to confirm the correct wire functions.