Troubleshoot Trailer Wiring - Left Signal and Brake Lights Not Working

This is a practical approach to troubleshoot any electrical wiring problem with a trailer. The diagnostics start with an inspection of the tow vehicle's electrical system. A diagnostic tool is reviewed and fuses are checked. A multi-meter is used to check DC voltage. Our boat is used in saltwater and corrosion issues on wiring connectors are addressed. Try and check simple issues first like a bad light bulb. Don't rely on a visual inspection of the bulb. Install a bulb that you know is working.
There should be no reason that you would have to pierce the insulation on one of the trailer wires. If you do, it will have the potential of allowing corrosion to form. Seal the hole with some type of sealant. Electrical tape will not be sufficient to prevent corrosion over time.

[@ALCusick]

Great video. Walks through common sense steps to find problem, with good videography and great vocals, all tied together. outstanding

[@landrytheaveragereasonable6735]

Thank you for taking the time to write that polite comment.

[@johnjwalker5820]

I would have never thought to check fuses. Thanks big help

[@landrytheaveragereasonable6735]

You're welcome. Thanks for the comment.

[@camiwilson6491]

you're better than my local boat repair shop

[@landrytheaveragereasonable6735]

Thank you for the nice comment.

[@062809]

Thank you for taking the time. Great learning experience.

[@landrytheaveragereasonable6735]

Your welcome. Comments like yours are the very reason I made the video.

[@rgorji]

Thank you. This is a very logical way to help figure out issues wit hthe lights.

[@landrytheaveragereasonable6735]

I would like to take credit for the 'logical' part but, all I did was contact the trailer manufacturer and asked them how diagnose the problem. I simply made a video from their advice. Glad it has helped as many as it has.

[@brianmorgan4977]

Thank You Thank You Thank You. Replaced the light bulb ,and wow. Like you said. The bulb didn't even looked bad.

[@landrytheaveragereasonable6735]

Nice job...life suddenly becomes wonderful again.

[@conservativeriot5939]

Thank you. Mine was also just a bulb issue. After I checked all the wires and fuse and cleaned everything.

[@landrytheaveragereasonable6735]

That's usually the way it works. Glad it all worked out.

[@brentonatkins]

Thanks for this!

[@landrytheaveragereasonable6735]

You're welcome. You saying 'thanks' makes me feel great about making the video.

[@MachTuck]

Thank for sharing the video Landry, I have a problem with my left turn signal and LH flasher, running lights work on both sides, but no LH turn signal nor flasher, truck is good, I got power in the plug for turn signals, any suggestion on what to check? thanks again

[@landrytheaveragereasonable6735]

That sounds similar to what my problem was. Do you have two filaments in the light bulb? Maybe one of the filaments is bad. I would welcome any comments from other viewers.

[@MachTuck]

@@landrytheaveragereasonable6735 Thanks for your reply Landry! I switched bulbs, same thing, Im going to check the ground connection in the lamp next.

[@YouTubegirlLetsgetstarted123]

Video was great. Thanks

[@landrytheaveragereasonable6735]

Thanks for the feedback

[@domalbe51882]

Thank you so much, Sir, for sharing.

[@landrytheaveragereasonable6735]

Sharing life's experiences is a beautiful thing. I'm glad you got some benefit out of this video.

[@idmhead0160]

Thanks for the pointer on the light bulb. I just replaced the 4 connector wiring on my 2000 GMC Jimmy. The old connector was corroded up, and then I found that the crimp connectors that hooked that wire to the wiring that came with the vehicle were corroded up too. I replaced that and used an LED tester similar to yours. Left and right turn signals worked. However, the right turn signal on the boat trailer doesn't work. Nor the brake light on that side. I will check the bulb tomorrow. I was thinking maybe it just wasn't getting enough voltage. Hopefully, I will luck out and it will just be the bulb. However, I had a separate set of lights that you can attach to a trailer with magnets and those didn't seem to be working either. So, probably it's some other problem. The wiring from the vehicle had 6 wires. Two were taped off and not used. I think my dad did that when he wired it up 20 years ago. As far as I know, they aren't needed as the signals were working before. I'll have to check the fuses. But, the LEDs flash on the tester. So, I don't know how it could be that. Probably, it's a bad connection somewhere.

[@RogerPack]

Did you figure it out in the end?

[@idmhead0160]

@@RogerPack Unfortunately, no. I need to revisit it at some point.

[@לאידועלאידוע-ש1ז]

Question. i have an 02 Dodge Ram 1500. My 4 pin flat connecter on vehicle for trailer works fine. EXCEPT THE RUNNING LIGHT. My 7 pin connector on vehicle for trailer works fine. EXCEPT THE RUNNING LIGHT. What do you recommend? Thanks.

[@RogerPack]

Did you figure it out in the end?

[@warrenlouisiana2277]

Thank you larry, this made me do some thinking

[@landrytheaveragereasonable6735]

Your welcome. Thank you for taking the time show your appreciation.

[@spacecoastbonsai1421]

What if I have LEDs? My left side running lights are working but no brake no blinker. The right side all three are working

[@landrytheaveragereasonable6735]

I would guess that the approach should be similar. It could be a bad LED (which I don't know how to test for) or there is a bad wiring connection. We would all be grateful if you would follow up on your efforts.

[@ScarFace405_]

What if my driver side lights blinker work but not the brake light. Everything works except for my driver side brake light.

[@landrytheaveragereasonable6735]

Hi Mark. Because I'm not an expert in this area, the best advice I can offer you is to type into the KZbin search bar exactly what you commented to me. Hopefully you can find someone who has covered your exact issue. Some people do a better job of explaining too. Good luck.

[@BobbyHTTC]

Very helpful...thanks!

[@landrytheaveragereasonable6735]

You're welcome, thanks for the feedback.

[@travisgeerts3241]

Awesome video!

[@landrytheaveragereasonable6735]

Thanks for the strong comment, you made my day.

[@helenachase78]

my wires are all taped up . fricken mess.

[@shaanvirao2071]

Thank you very nice

[@landrytheaveragereasonable6735]

Thanks for the positive feedback

[@artamus73]

They make a nice cheap relay tester now, works great.

[@landrytheaveragereasonable6735]

Thanks for sharing. If you want to mention a brand name or where you got it, that would be great too.

[@idmhead0160]

BTW, a tip on cleaning up the connections. I ran across another video where someone recommended using a "bore brush" to clean the female part of the connectors. It's a little wire brush that's normally used for cleaning gun barrels. I tried it on mine, but, it was too corroded. 22 caliber seemed to be the correct size. I also tried using electronic contact cleaner, but, it didn't seem to do much.

[@landrytheaveragereasonable6735]

Thank you for the feedback. I hope others read it as well.

[@melbaacey2936]

Very helpful! Thanks for being reasonable ;)

[@landrytheaveragereasonable6735]

Glad it was helpful. Thanks for saying that.

[@helenachase78]

awesome job

[@Data4664]

Thnxs!!

[@landrytheaveragereasonable6735]

You're most welcome.

[@helenachase78]

very helpful

[@landrytheaveragereasonable6735]

Thanks for all your comments.

[@helenachase78]

Well its -30 this morning in Saskatchewan and I just cleaned my 4 pin connection . The 3 o'clock one and thanks to you I will not get pulled over !

[@landrytheaveragereasonable6735]

You're the one that gets the credit but, I'm glad to be part of the success.

[@satsingh6094]

Very informative thank you

[@landrytheaveragereasonable6735]

Your very welcome. I'm glad it helped.

[@ApriliMille]

bad ass boat

[@landrytheaveragereasonable6735]

It's been a lot of fun

[@gabrieljfox]

Thank you it was a fuse.

[@landrytheaveragereasonable6735]

Sorry for the late reply but my Notifications on KZbin are not notifying me of new comments. I'm glad things worked out for you. Thank you for commenting, really great to get feedback.