Extra Blue Wire Near 7-Way Trailer Connector on 2003 Chevy Silverado 2500 HD

Updated 06/28/2026 | Published 05/26/2019

Question:

I have a 2003 Chevy Silverado 2500 HD gas truck. My new puppy chewed the wires behind the trailer wiring plug. I know where all the wires go into the plug, but there was a blue wire by itself. I cannot find where it goes. It has a piece of a plug on the end of it. I’ve looked up on the frame to see where it went. Can’t find anything. Can you help me ? Thanks I just sent my question with a picture. The lone blue wire does not go to that plug. It has to go somewhere else. Thanks again

asked by: Jessey B

Expert Reply:

I'm pretty sure that's to wire up a third brake light on a camper shell. To know for sure, take a circuit tester, like our part # PTW2993, and test that wire while applying the truck's brakes. If I'm correct it's a dedicated brake light wire and it doesn't need to be connected to anything unless you have a camper shell with a third brake light, you need to connect to it. Without the shell it's an extra unused wire.

expert reply by: Charles S

click to enlarge

Hank

6/20/2024

Tested and true extra brake light wire.

Ross M.

5/4/2026

My dog must be related to his, but the connector is chewed off , would the bare wire affect my drl’s?

Tim B.

6/28/2026

@RossM I have the same harness. Someone severely over attached many connectors under the truck to get 4 pin wiring and cobbled it together. The 7 pin wasn’t fully working. Do you know which wire is the ground in that setup that goes to the 7 pin. There is no white wire so I just wanted to check.