Code scan reads “Open left tail light circuit”
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Registered User
Joined: Dec 2005
Posts: 81
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From: Elk Plain, WA.
Code scan reads “Open left tail light circuit”
I have no left turn or brake signal on my trailer; replaced the trailer plug socket on the truck and still nothing. Code scan reads “Open left tail light circuit” DOES ANYONE KNOW WHAT THIS MEAN AND HOW TO FIX THE PROBLEM? I had to leave the trailer 80 miles upstate because of this and need to get it home. 
Cummins Guru
Joined: Feb 2008
Posts: 4,191
Likes: 65
From: Sunny Southern California Land of Fruits and Nuts
possible relay
All vehicles are equipped with two trailer tow relays, one for the trailer right turn and brake lamps and the other for the trailer left turn and brake lamps. The trailer tow relays are conventional International Standards Organization (ISO) micro relays. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions. Each relay is contained within a small, rectangular, molded plastic housing and is connected to all of the required inputs and outputs through five integral male spade-type terminals that extend from the relay base plate.
The trailer tow relays are located in the Power Distribution Center (PDC) in the engine compartment near the battery. Refer to the layout label on the underside of the PDC cover for specific relay cavity assignment information. A trailer tow relay cannot be adjusted or repaired and, if faulty or damaged, the unit must be replaced.
All vehicles are equipped with two trailer tow relays, one for the trailer right turn and brake lamps and the other for the trailer left turn and brake lamps. The trailer tow relays are conventional International Standards Organization (ISO) micro relays. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions. Each relay is contained within a small, rectangular, molded plastic housing and is connected to all of the required inputs and outputs through five integral male spade-type terminals that extend from the relay base plate.
The trailer tow relays are located in the Power Distribution Center (PDC) in the engine compartment near the battery. Refer to the layout label on the underside of the PDC cover for specific relay cavity assignment information. A trailer tow relay cannot be adjusted or repaired and, if faulty or damaged, the unit must be replaced.
Administrator/Jarhead
Joined: Jun 2006
Posts: 14,971
Likes: 19
From: Jonesborough, TN
You also need to make sure that the wires are not pinched under the bed or spare tire. Had that happen to me once, rear lights went nuts. Just get under the truck and follow the wires from the lights back.
With that relay above, you should be able to find one that has the same ratings in your power distribution block to swap it with to test.
With that relay above, you should be able to find one that has the same ratings in your power distribution block to swap it with to test.
Registered User
Joined: Nov 2011
Posts: 4,479
Likes: 211
From: Isanti, MN
You also need to make sure that the wires are not pinched under the bed or spare tire. Had that happen to me once, rear lights went nuts. Just get under the truck and follow the wires from the lights back.
With that relay above, you should be able to find one that has the same ratings in your power distribution block to swap it with to test.
With that relay above, you should be able to find one that has the same ratings in your power distribution block to swap it with to test.
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