Trailer Wiring Check (Problems and Solutions)

Do you randomly and often get a "Check Trailer Wiring" or similar message in your truck driver information center? Let's see if I can help you diagnose.

Finding the cause of an error message related to your trailer wiring can be difficult. You may have tried several ways, but still did not find the cause, and the message appears again.

There are several possible causes as well as solutions (see table below). This could be the trailer plug, wiring, connectors, trailer brake fuse, emergency stop pin, ground connection, or near the brake drum. There are solutions for every possible cause if you know where to look.

Possible cause or cause	Solutions to try (if applicable)
trailer fork	Attach the wires to the pins. Clean the contacts with a wire brush. Secure the wires in place. Change your fork.
trailer wiring	Replace broken wires.
Electrical connectors	Clean up corrosion areas. Reinstall the connectors securely.
Trailer brake fuse	Replace blown fuse.
Tear-off switch pin	Replace switch pin.
Grounding	Change land. Replace ground wire.
Brake drum clamps	Replace damaged magnet. Replace damaged wiring.

Here I have mentioned some common reasons why trailer wiring might not work and will provide you with some solutions in more detail.

Possible causes and recommended solutions

Check trailer fork

Check the plug in the trailer. If the contacts seem weak, use a wire brush to clean them. If they are not securely attached to the pins, secure them properly. Try replacing it with a higher quality brand name model if it's a cheap fork.

If you have a 7-pin and 4-pin combo plug like the newer GM trailer models, this could be causing the problem if the 7-pin plug is on top. While you might find this combo arrangement convenient, and the combo plugs attach well to the bumper, it only works well if the 7-pin plug is on the bottom and the 4-pin plug is on top.

When the 7-pin part is oriented normally, the trailer brake and ground connectors are the bottom two terminals. The problem is that the two wires connected here are loose, loose and can easily lose contact and reconnect. You should check this plug if you see intermittent warnings to disconnect and reconnect the trailer wire. Try tapping on the plug to see if the message is still displayed on the DIC.

In this case, the solution is to reinforce and protect the wiring connected to the bottom of the 7-pin plug. If necessary, use electrical tape and ties. Alternatively, you can replace it with a blade or trailer-side Pollak connector, such as a Pollak 12-706 connector.

Inspect the wiring

Inspect trailer side wiring and wiring outside trailer conduit. Trace the wires to check for breaks.

Check connectors

Check all electrical connection points under the bed. If they are corroded, clean them with sandpaper and lubricate with dielectric grease, or replace if the corrosion is too great.

Reinstall the connectors securely. You can use a zipper to make them secure.

Check trailer fuse

Check the trailer brake fuse located under the hood. If it is burned out, it must be replaced.

Check disconnect switch pin

Check the breaker pin.

change land

Try changing the ground from the battery to make good contact with the trailer frame. Using dedicated land rather than shared land may be better. If the ground wire or ball is too light, replace it with a larger diameter wire.

Check brake drum clamps

Check the clips on the emergency brake drum at the rear. If the magnet is damaged, replace it, and if the wiring is kinked or damaged, pull it out and replace it, ensuring a good straight connection.

Even if only one, two, or three of the four trailer brakes are working, you may not receive a "Check Trailer Wiring" DIC message. In other words, the absence of this indicator does not necessarily mean that everything is working correctly, or the message may be intermittent.

Are you still seeing the error message?

If you're still having a hard time identifying the cause of the problem, have someone sit inside the truck and check the trailer indicator while you move every part of the entire chain.

If you notice that the error message only appears when you move a particular part or component, you will know that you are approaching the exact location of the problem. Once identified, read the section above about that particular part.

Take a look at some of our articles below.

• What happens if the ground wire is not connected
• What are spark plug wires connected to?
• How to test trailer brakes with a multimeter