How to Install a Standard 7-Way Connector on a Semi-Truck

Updated 10/30/2025 | Published 02/22/2025

Question:

trying to hook a seven way plug to the back of a semi for Trailer lights and brakes. The problem I am having is the wires going to the back of the semi have a separate wire for the directionals and a separate wire for the brake lights how do I get this to work with a regular seven way plug?

asked by: Bo R

Expert Reply:

Hey Bo! To set up your semi for a standard 7-way plug, you will first need the Curt Powered Tail Light Converter item # C59496, which would tap into the circuits feeding your tractor trailer 7-pin round plug. The yellow wire taps into the feed for the left turn signal, the green into the right turn, the red into the brake, the brown into the running light circuit, and the white wire would ground to the truck's frame. The black wire connects to the positive battery terminal.

Once the Curt item # C59496 is installed, you will then use the Hopkins item # 37185. The 4 pole from the converter would plug into the 4 pole on the adapter, then there will be four loose wires to connect. Ground the white wire, the black wire connects to a 12-volt power source, the blue wire is used to carry the output voltage from a brake controller if the trailer has brakes and the purple wire is usually used for reverse lights. Other than the ground, if the other three wires aren't needed, you can bundle them up out of the way.

expert reply by: Jerred H

Jerred H.

10/30/2025

Hey Bo, how did things go after wiring the Curt tail light converter and the Hopkins adapter on your semi? Did that setup get your trailer lights and brakes working together correctly? Your update could make it easier for others tackling the same wiring issue.