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Ford F150 Trailer Running Lights Not Working – [5 Easy DIY Fixes]

You and your buddies want to go fishing, but your Ford F150 trailer running lights not working! And, it’s a big problem. So how do you troubleshoot and fix the trailer lights?

Don’t fret! I am here to help you fix the trailer tail lights. In this article, I will discuss all the possible reasons why the trailer running lights are not working on your Ford F150 and how you can troubleshoot and fix them.

One of the common reasons why the trailer lights are not working is the blown trailer lamp fuse on your Ford F150. Other reasons include poor ground connection, faulty trailer connector, faulty electrical harness, and bad light bulb.

Please Note: You can follow this troubleshooting guide for any Ford F150 model.

Common years include Ford F150 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017.


5 Reasons Why Ford F150 Trailer Running Lights Not Working!

Here are the five possible reasons why the trailer running lights are not working when connected to your Ford F150.

ProblemSolution
Missing trailer lamp fuseInstall an appropriate one
Bad trailer lamp fuseReplace the fuse
Bad serviceable trailer light relayReplace the relay
Bad non-serviceable trailer light relayReplace the fuse panel
Bad trailer light bulbsReplace the tail light bulbs
Loose trailer connectorClean and reconnect it properly
Bad trailer connectorReplace the connector
Poor ground connectionScrape some paint, and ensure good ground contact

1. Missing or Bad Trailer Lamp Fuse

The most common reason why the running lights do not work is the missing or blown trailer lamp fuse.

The fuse position varies from gen to gen for Ford F150, for example, Fuse #53, Fuse #55, and Fuse #67.

To find out the exact fuse position, check your owner’s manual. If the trailer light fuse is blown or even missing, you need to get a new one and install it.

After replacing the faulty fuse, hopefully, you’ll get the trailer parking lights working again. You have multiple fuses on the fuse box under the hood for various trailer light functionalities.

You need to make sure all of them are good for all the functionality to work correctly. The fuse numbers regarding the trailer lights are mentioned in the owner’s manual.

2. Bad Trailer Light Relay

If your Ford F150 has relays for the trailer lights under the hood, you need to ensure they are in good condition. 

To find the exact relay numbers for the trailer lights, you need to check the owner’s manual. If the relay is faulty, you need to replace the relay to fix your trailer running lights.

Some models have trailer light relays baked on the board and are not serviceable. But they don’t go bad so often, and if you need to replace those non-serviceable relays, you will have to get a whole new fuse panel.

3. Bad Trailer Bulbs

If your trailer has those old incandescent bulbs, you need to ensure the filaments inside them are not broken. To verify the bulbs are fine, open up the cover and do a visual inspection.

If you find the existing ones are bad, replace them to fix the problem. I recommend you upgrade to LED lights for your boat trailer.

They are durable, properly sealed, and rated for higher service hours than incandescent bulbs.

4. Trailer Connector Issues

A bad or loose trailer wiring connector can cause the trailer running lights not to work as intended.

To eliminate the connection issue, unplug the trailer harness from the wiring connector socket. Then clean the socket, the trailer harness connector, and the harness connector behind the bumper.

Remove all kinds of dirt, debris, and rust. You can use dielectric grease to reduce future corrosion and reconnect them properly. And, if it’s a connection issue, reconnecting them properly will fix the problem right away.

If that doesn’t bring back the running lights, it could be a no-power issue on the connector. If the trailer connector doesn’t have proper voltage, the trailer lights won’t work correctly. 

On the 4-way flat connector, the immediate next pin to the ground connection is for your trailer lights. And, on the 7-way connector, the pin at the eleven o’clock position controls the running lights of your trailer.

For both the connectors, you can use a trailer wiring tester, a multimeter, or a test light to verify whether the running light pin gets proper voltage from the battery when the engine is running, and the lights are turned on.

If the test light does not light up, or you don’t get proper power on the running light pin, the connector socket or the electrical wiring of the connector may be faulty. 

Disconnect the electrical harness connector from the back of the trailer socket on your truck and test the pins. If you get proper voltage in the harness, the trailer wiring connector socket is faulty.

In that case, you need to replace the connector socket.

On the other hand, if your 4 or 7 way socket is fine, it might be the trailer harness you need to replace. To verify, you can connect the trailer to a different vehicle.

5. Poor Ground Connection

If your trailer lights do not work on the Ford F150, you may have a poor ground connection.

This can happen if the trailer’s frame has a thick layer of paint or rust. Hence the ground wire has poor contact with the metal surface of the frame.

If your trailer lights have individual ground cables (white), make sure they are grounded to the frame of the trailer through the studs.

Some lights don’t have any ground wires. Instead, the studs of the lights work as the ground connection. To make sure the studs have good ground contact, sand off the holes to remove the paint and rust with sandpaper.

Also, make sure the white cable of the trailer harness is correctly grounded to the metal surface of the trailer frame.

After you ensure a proper ground connection, hopefully, you will get the Ford F150 trailer running lights working again.


Final Words

So there you go. Now you know why your Ford F150 trailer running lights not working. So go ahead and troubleshoot according to this guide, and hopefully, you’ll be able to fix the lights.

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Kevin Shaw

Editor-in-Chief at F150Lab

Kevin Shaw has a vast knowledge of pickup trucks, especially the Ford F150. He has been doing various DIY fixes, upgrades, and modifications to pickup trucks for more than five years now.

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