A trailer plug is essential to have on your truck. Whether you tow a travel trailer or a boat trailer, having a functioning trailer plug is important.
Your trailer plug is responsible for providing power for your trailer wiring. Trailer lights, running lights, and even your turn signal need power from your trailer plug.
But what do you do if you have no power at your trailer plug? This post will review the possible issues and solutions to get your trailer plug back in working condition. We will review the most common causes of no power at your plug, including:
- Ground Wire
Knowing that the issue is total power missing from the trailer plug gives us a clue where to begin. I also like to start with the most common and simplest fix to a problem. In this case, the most common cause is a bad ground wire. So let’s start with that first.
Table of Contents
If you are not getting 12V power at your trailer plug, the most common issue is a bad ground wire. Why? It’s pretty easy when you think about how 12V power works. Whether you have a truck or trailer battery, you need a positive and negative power source to make things like lights work on your trailer.
A light or any other 12V-powered appliance will not work without the positive and negative wires. That leads us to believe that if you are not getting any power, it may be an issue with either the positive or the negative (ground).
It is more common to have an issue over the ground wire vs positive (hot) wire. The ground wires are usually more exposed to the elements and more susceptible to corrosion and a bad metal-to-metal connection.
Here is another reason the ground is most common when the plug is not working.
A 7 pin connector has several wires with separate wires that control your tail lights, running lights, and even your electric brakes. Each of these wires is a positive (hot) wire. And the only wire they have in common is a ground wire on your connector. So if you have no power at all, the usual issue is the shared common ground wire. That means if the ground wire gets disconnected, all the rest of the lights go with it because they don’t have sufficient negative ground from the battery.
Check your ground connection. Follow the wire from your truck battery to your trailer plug. Visually inspect for any signs of a broken wire or rodent damage.
Also, check the connections where the ground wire screws to the frame. Since this is exposed, it could have excessive corrosion and not cause a good metal-to-metal connection.
For a more in-depth guide, visit my post on how to check trailer ground wiring.
Above, we reviewed that the negative ground wire is the most common cause. What about the positive wire? Does that cause a problem? The answer to that is “yes,” but not as likely. The reason that the positive wire is not as likely the issue is that you have multiple positive wires for each individual light. Also, you have separate fuses for each turn signal, backup light, and running light.
The below photo is the fuse box from my GMC Sierra.
You will see that there are separate fuses for each one of the lights we just reviewed. If there is no power to your trailer plug, the solution is a more universal problem that covers power to your entire plug. Although it does happen and fuses burn out, it is worth a quick test to see if your fuses are good.
Take off your fuse panel. Each fuse is labeled on the panel like a wiring diagram. Each is marked with a number which is a fuse and which is a relay. Find the fuses associated with your trailer plug.
Get a multimeter and check for continuity between the two back pins of the fuse. A fuse is a wire rated to disconnect at a certain voltage to disconnect the circuit to avoid damage quickly. If you have continuity, then the fuse has not been blown, and the power was not disconnected.
Here is a quick way to do it with a test light or reading voltage. Put the black or negative probe on the negative terminal of your battery. Or you can even attach it to any metal part of the engine. Then place your positive probe test light or multimeter on the back of the fuse pin. Do this to both pins, one at a time. You should get 12V at each pin.
If the ground wire and fuses look good, the next step is to look at the connector itself. The connector is comprised of a plastic trailer socket with metal pins and a wiring harness connected to it. With the connector, the usual issue is either the metal pins or the harness connecting wires.
The metal pins in the connector can either get bent or expand larger than the receiving pin. When this happens, the connection is too large, and there is no solid metal-to-metal connection from the truck to the trailer plug.
Also, the harness wires that lead into the trailer plug could be loose, not offering a good connection to the pins.
Inspect your trailer socket and look for any pins that are either bent or where the gap is wider than the others. If you see any out of the ordinary, gently see if you can bend back and close the gap.
Inspect the wiring harness and confirm the wires are secure into the connector. Give each a light tug to make sure that there is a firm connection to the trailer plug.
No power to your trailer plug will leave your boat or travel trailer without lights or electric brakes. Even if your vehicle lights are on, your trailer will need power. A bad ground wire is the most common cause of power failure in your trailer plug. The next thing to check for is the truck fuses and the trailer connector for straight secure metal pins.
Tony is an avid camper and RV traveler. He fell in love with camping on his first RV trip with his wife over 25 years ago. Tony loves sharing lessons learned and tips about RV maintenance and safe traveling.