How to Troubleshoot Trailer Lights that are not Working

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In this video I will be showing you how to troubleshoot #trailer #lights, this included everything right at the vehicle lights, all the way down to the lights on the trailer and everything in between.

When I bought this trailer, the lights were acting up. These are the original incandescent lights, newer trailers may have LEDs, the same process does apply. As you can see the signal light is acting up. When I move the connection, the light then starts to work.

Once I pulled apart the harness on the truck, I found crimp connections were used and typically I’m not a fan of these. If the crimp isn’t tight enough which is what the case was here, there won’t be a good connection and eventually, the wire will pop out. Next is that crimp connections don’t provide a weatherproof seal unless you use the heat shrink style, but they can be expensive to purchase or at least where I live.

Using a test light, this can determine if there is power at the connection. Turn on your parking and hazard lights, the hazard lights will activate both the left and right turning signals. Connect the test light to the ground terminal, this is the exposed one. Then probe the other three terminals. The test light should illuminate solid for the parking light and flash for the signal lights.

If nothing is lighting up, then there may be a poor ground. Find an alternative ground for this. If it’s still not working, some of these have a module so it may be faulty, or there may be a faulty to where the trailer harness is connected to the vehicle. Inspect the wire’s insulation for any damage as well, this would allow in moisture causing breaks in the conductor.

Hooking up the trailer connector, as you can see the wires have already been cut from when the trailer was brought home. Make sure you don’t cross the bare conducts, use electrical if needed. If they cross, they may blow a fuse on the truck. Make sure you do inspect the wires and connect on the trailer end as well.

Clip the test light to the exposed ground wire. Once connected, I can check the exposed conductor past the plug to ensure it’s working as well. Do no pierce the casing as this will cause a spot for moisture to get in, causing the conductor to corrode and cause another failure down the road.

Inside of testing past the plug where I have the wires stripped, you can check at the light instead. This would involve removing the light, either the bulb or in this case the whole assembly. There may sometimes be a plugin the back to disconnect or you may have to remove the bulb. With the lights on in the truck and the connector plugged in, probe the plug or bulb socket. If you are finding an issue between the plug and light, there’s an issue along the wire somewhere, or there may be a ground issue. You can replace the whole wire or there are kits you can purchase which replace all the wiring.

As for fixing the problems I have here. First is cutting the wires to length and removing the spot where the issue was. Try to pick a good area where the copper wiring is shinny, discolored copper will indicate it’s been exposed to moisture won’t give a good connection.

Strip the wires as needed.

If you can’t cut it back any further, clean it with a scuffing pad. Before the wires are twisted together, in order to achieve a waterproof repair, I’m using an adhesive filled shrink tube. I have a kit so I can select the correct size based on the wire used and cut it to length using side cutters. This needs to be installed before the connection is soldered. Another option would be liquid tape, but it doesn’t apply as cleanly.

Twist the wires together on the truck side, I used rosin core solder which does clean the wire to some extent as well. For the connections, I’m using a western splice which is a commonly known type of soldered connection.

Apply the center shrink over the connection, make sure it’s centered on the joint. Using a heat gun, warm the heat shrink. When the casing is heated, it’ll shrink and melt a sealant that adheres to the existing casing, making a waterproof connection.

On the trailer side, twist the wires together and soldering the connections which is what I’ve already done here. Again apply the heat shrink. Make sure that heat shrink is installed before soldering the connection.

The wires are put back in their split loop casing, this protects the wiring from any road debris. Electrical tape is used to close up the casing so the wires can’t come out. And finally, it’s installed back onto the trailer tongue. Verify that the lights are working and you’re set.

© Homes for Beginners 2019
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No part of this video or any of its contents may be reproduced, copied, modified or adapted, without the prior written consent of the author.

[flossfly]

Thank you for helping all the people who have a trailer light issue. Am about to tackle a faulty trailer and have some solid info. Thank you!! The internet is a mixed blessing but stuff like this is gold.

[nutnfancy]

Excellent: clearly filmed, succinctly narrated, well done!

[RiverRat]

You’re the man solved my problem- bad ground at the wiring to brake light connection

[thomasjensen]

kick ass dude! TY! having it clearly explained and layed out really takes the worry out of the equation. subscribed!

[MrAvh]

Gave me some additional ideas on how to troubleshoot and repair the lighting system! Thanks! (soldering, shrink tubing, plastic casing.)

[dido]

Hi there, thanks for the great video. I really appreciated that you had video transcribed for clarification.

[carolemcconnell]

This video was exactly what i needed.good explanation.thanks for sharing!!! Deer hunter 101...

[bennierheeder]

This was super helpfull. Thank you, it sorted my problem out.

[jackherbic]

I like your channel you do the how to genre perfectly

[beardedbiker]

Glad I found this, I have a small trailer that apparently was wired from 7 way to 4way flat. It had single bullet connectors with the extra wires soldered to the outside of the connectors, Unfortunately when I unwrapped everything only the ground was still connected and I’m trying to find my running lights with only a blue, red, and black wires left to connect.

[robcote]

You've done a great job thank you for that !!!

[HNXMedia]

Solid video! Nice presentation! Total pro!

[rolandmetayer]

Very well done ! Thank you. Cheers from Canada.

[lindamuvic]

Thanks, first thing I did was pull my white wire out, so my connection would reach my truck.

[mattsmith]

This is very informative!
When it comes to wiring trailer lights though, I cut the "Y" harness, clean through, and install Deutsch (DT) connectors at every light. This way, when I go to replace a burned out light, I only have to crimp one side of the wire and I don't have to worry about replacing (and re-routing) a whole new wire. Even if I have to replace lights frequently, because of this connector, the length of my original wire stays the same length, as I'm only replacing the short amount of wire leading to the light itself.
I admit, it is more expensive, but on the positive, you don't have to spend $75 and 4 hours in your garage when something goes wrong.
Lastly, if you buy Hopkins trailer brake lights, replace those disgusting, mushroom cap, cheap steel bolts with stainless steel, hex head bolts (1/4"-20 - 1.25" length).
Can we PLEASE put an end to the "guuud enuuff" people!?!?!?!

[coltcele]

This was a great video. I bought a test light, and I learned here I learned here I had the ground on the wrong lead on the truck side. My brake/hazards are fine, getting power. The lead for them at the truck side isn't getting power. Any thoughts why this is? Thanks in advance!

[stevesaviano]

Well done, great info, BUT... I believe my issue originates at the back of my Class A RV. My 7 way cord works properly when plugged into the back of my friend’s pick-up, connecting to my car. But I get absolutely nothing when I run it from my RV to my car. Any ideas or suggestions on where the problem is, and how to repair it?

[garthtimmins]

Trailer lights are not very complicated, and yet I am always surprised by how many people there are who are towing trailers with non-working lights.

[rememberme]

Thanks, it is helpful, but my trailer turn signals and break lights works when I use signal or break, but they should turn on as soon I turn headlight on that is the problem I am having, if any help I will appreciate.

[russellburton]

All lights are good on the truck side as well as the running lights