How To Repair or Replace 4-Wire Flat Trailer Wiring Connector Harness

Learn how to repair a trailer wiring harness that was damaged when borrowed by someone who did not connect the wiring to their vehicle. This is a very simple and easy repair, but does require a few items that you may not have:
Materials needed:
New wiring harness to replace the one that was damaged
Heat-shrink insulation tubing
Solder
Tools required:
Soldering iron
Wire cutters
Wire strippers
Heat source such as a blow torch, lighter, or heat gun
Here are links to items used in this video. Clicking these and buying something will send a few pennies to help this channel, and does not cost you anything extra:
Inexpensive Soldering Iron: amzn.to/33hOd5I
Assorted Heat Shrink Tubing: amzn.to/2rfb5oj
Trailer Wiring Harness: amzn.to/2PJz0Gq
#TrailerWiring #TrailerRepair #TrailerElectricalConnector
Music used in this video:
"Wishful Thinking" by Dan Lebowitz
"Michigan Greens" by Dan Lebowitz
"Jeremiah's Song" by Dan Lebowitz
"Glen Canyon" by Dan Lebowitz
"Firefly" by Chris Haugen
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[@freedomfighter2911]

Great vid.....please remember to cross your hitch chains. Why? If your hitch ever pops off the ball... the crossed chains will catch the trailer.

[@AmplifyDIY]

+freedom fighter this is an excellent suggestion. Thank you!

[@noahbielejeski9194]

freedom fighter sss##sx

[@Brandala182007]

I had the same thought as soon as I seen it!

[@user-cv3gd2wr5q]

freedom fighter see, now that is a great comment on your part! You said what he did wrong and not only said how to correct it BUT also the reason WHY. Thank you for that sir.

[@David-fv7zg]

True......please dont ask me how I know.....LOL

[@fernandoreyna6551]

2 in for 1 video. Awesome. I would add links for tools used. Very Helpful.

[@ullipaul6684]

Thanks for the video I fell confident that I can tackle this project.

[@noneofyourbusiness8092]

I like the way you tied the wires together. I will now copy from you.

[@greggsanchez9768]

Saved me from a ticket! Thanks a lot man! I’m a beginner at a lot of things and you explained very well. Awesome video

[@adrianlarsen1106]

One other thought: Soldering and heat shrinking the wire is the RIGHT way to do this. Those crimp butt connectors are just endless problems. If you solder and shrink, it's a lifetime repair. (Though I'll admit I cringed a bit with the open flame for the shrink. Yes, it works fine in a pinch, but I always prefer a heat gun whenever possible. Better, safer, and more uniform shrink.) I also recommend the heat shrink with the adhesive inside. It's like hot glue that heats up and seals the entire length of the heat shrink.

[@sea8bass]

Awesome video - about to undertake the identical repair on my trailer. So, very helpful!!

[@AmplifyDIY]

Good luck!

[@greenz59]

This dude has the most fantastic of repair musacs

[@grethstixx8078]

Great vid.

[@ashleymichalosky3547]

Super helpful! Exactly what I needed to learn with the perfect amount of detail! Thanks for your videos!!

[@AmplifyDIY]

You're very welcome, Ashley!

[@DrewJacobson61]

Good technique and great narration ❤️

[@garya1625]

well done, i'll be soldering from now on...

[@DorianPryke]

I went and watched this video because I need to replace the other end of it on my 2012 ford escape😂 I got real excited when I saw that’s what you backed up to the trailer. Glad to see I’m not the only one putting my escape to work

[@AmplifyDIY]

My Escape was a 2008, and I loved it! I've moved on to something else since making this video, but I really loved that vehicle, and I put it to work all the time! Thanks for watching. :)

[@dgc7321]

good video...thank you.

[@MikeJones-jf7lx]

Great Video, thank you....

[@protectyourcar5889]

Beautiful trailer^^

[@hank10983]

Great video ,have to go replace my trailer wire harness,thanks

[@AmplifyDIY]

Glad you liked it. Thanks for watching!

[@InternalTaiChi]

Thank you. I just got my new camper and needed to connect the 4 pin. I had no idea how to do it. Your video was a big help!

[@AmplifyDIY]

Glad it helped!

[@tedbaxter5234]

Thank you!

[@MCL20242]

Worked perfectly great video!

[@AmplifyDIY]

Great to hear, Milton!

[@SozoSeasonFreedom]

Good, quality video. Thank you

[@AmplifyDIY]

Many thanks!

[@kellytenhove5023]

Thanks for the video. I might just test out the lights before soldering in case they are crossed to avoid possible extra work.

[@AmplifyDIY]

That's a very good suggestion. Thanks!

[@dougbonawitz1718]

For newbies, make sure you solder out in front of your face and not below so you don't inhale the fumes!! :-)

[@AmplifyDIY]

Fantastic tip. Thanks!

[@adrianlarsen1106]

Great job. You are correct that the wiring colors are standard across all trailers. Right turn/brake is Green. Left turn/brake is Yellow, tail/marker lights are brown and ground is white. Makes it easy to get things right when the colors are always the same!

[@tommydamico1796]

what do you do when theres an extra yellow wire

[@AmplifyDIY]

Hmm. I’d probably start by using a multi tester to check for continuity between the extra wire and the rest of the wiring harness. Next I’d try to trace it to see where it goes. Good luck!

[@adrianrosales9147]

How do you do when i put extra light...i need conect in Brown wire.

[@AmplifyDIY]

I'm not clear about exactly what you want to do, but you'll probably need a splitter of some kind. If you search google for "trailer wire splitter" there are lots of easy options. Good luck!

[@greywolfnc]

that's true till u come to ur left turns right, right turns left.had to cris cross them. plus wires coming out of new lights r red black green and white.

[@expansioniskeyrn]

Nice video! I like to it check to see if it’s working before soldering and covering it up*

[@AmplifyDIY]

Good call!

[@horacesawyer2487]

Nice trella

[@JoGeGoJr]

Neat job bud 👍🏽

[@AmplifyDIY]

Thank you! Cheers!

[@matthewwynne939]

I've had my truck for 16 years and have never towed a trailer (I've towed plenty of cars with a hook though), now I'm finally getting a trailer and noticed that the harness had been crushed. Thanks for the info.

[@enat]

4-pin connector, never seen that. In EU we used a 7-pin round connector, now a 13-pin. Nice work!

[@AmplifyDIY]

This style of 4 pin is really common in the US for smaller trailers. Larger ones have round connectors here - not sure if they are the same as in Europe. Probably similar though. Thanks for watching!

[@alwayssearching1882]

That's the correct way to solder. Great job.

[@AmplifyDIY]

Thank you for watching, alwayssearching!

[@alwayssearching1882]

@@AmplifyDIY Did my trailer today just like you did.

[@AmplifyDIY]

@@alwayssearching1882 Nice job! :)

[@greywolfnc]

I bought a new assy. for hooking a pigtail for my gmc 2005.ran my wiring for my camper trailer.I know green is for right turn and yellow is for left, put left turn signal on,right one comes on. my truck also has a 5 sec. shut off for my lights, camper lights stay on. tail lights have red, green and white. ive worked on a lot of trailers but this one has got me.

[@AmplifyDIY]

Hmm. Chasing electrical gremlins can drive you crazy! Sounds like somewhere along the circuit someone crossed the taillight wires. Just swapping them at the connector should get them working correctly. As for the lights staying on even when the vehicle’s lights are off: does your vehicle have back-up / proximity sensors? I had the same problem with a 2008 Ford, and needed to get a different version of the trailer adapter for the vehicle designed for one with the reverse sensors. Good luck!

[@loub8294]

Thank you

[@joshuamckillen3712]

Great video keep up the great work.

[@AmplifyDIY]

Thanks 👍

[@lp59pete]

Thank you.

[@AmplifyDIY]

Welcome!

[@sarahnordseth1131]

Thank you for putting out this helpful video! Would you be open to sharing what trailer you have?

[@ernestestrada2461]

Instead of placing the heat shrink on the short connector wires, the side on the trailer side were already single. Either way works, but I prefer to not do more work than needed. You should not use lead solder. Modern solder requires more heat so get a good soldering iron. If the wires have corrosion or charring, make sure to repair the source of shorting or it could start a fire. If it is just corrosion, cut back or replace wiring. Light corrosion may need flux to clean the wire so solder will flow and stick.

[@user-yv7fb8ki2v]

Nice video friend. I may have to take this route. Have a great day! thumbs up

[@AmplifyDIY]

Thank you very much!

[@user-yv7fb8ki2v]

I just realized this. What if its the female side that needs replaced. I had allot corrosion in mine. i had to soak in vinegar for a few hours which did a nice job, but appears according to the LED tester not a strong signal coming from for instance the left turn signal on the harness for trailer. additional corrosion or damage from the corrosion?

[@AmplifyDIY]

Both male and female versions of the replacement plugs are commonly available. The replacement procedure is the same for either one. Here is a good option to replace the female (vehicle) side: amzn.to/3kfa1Jq (affiliate link)

[@user-yv7fb8ki2v]

@@AmplifyDIY Thank you very much for your input. i appreciate that. Its inexpensive also. I was going to try fluid film first on harness, and ground first. If that doesn't work i may have to take this route. Thanks again. Keep up the good work on your videos.

[@user-yv7fb8ki2v]

@@AmplifyDIY i purchased that item. Still have problem. 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.

[@JohnJeiJei]

I'd add another tip for soldering - stagger your joins! Especially when you have so much wire available, staggering where each wire connects will prevent accidental shorts if a wire strand pokes through the heat shrink. Also, add enough flux to your wires, it prevents corrosion and the solder will flow much better.

[@AmplifyDIY]

Great tip, thanks!

[@blissfullibra]

What do you mean by "add enough flux"? I'm in the process of replacing mine and want to make sure I do a good job.

[@TheGreyGhost_of43rd]

😂 very unnecessary. If your time is money, like 99% of the population, disregard this comment

[@Phoenix36911]

Awesome vid seems easy…. I lend out my trailer and something similar happened 😅😂

[@AmplifyDIY]

Heh. People just don't seem to take care of borrowed stuff. Good luck getting yours fixed up!

[@noneofyourbusiness8092]

I use Liquid electrical tape to seal up the wires, instead of heat shrink.

[@brycelund4112]

Heat shrink is better. I use adhesive lined marine grade heat shrink that seals the connection perfectly. Liquid electrical tape is good for other things. I would never use it on a trailer wiring application. Especially because there could me small strands of wire sticking out from the liquid tape that could short against the frame or the other wires. Very unsafe especially if this happens at night. You won’t realize your lights aren’t working till you get hit...

[@ChaseDaPlaya]

Just so everyone knows, trailer wire colors are universal across the world, so a 4 flat connector wires all have the same color wiring that do the same thing by color everytime, and the trailer wires always match the colors

[@AmplifyDIY]

Unless, of course, someone has re-wired your trailer with the wrong color wires... 😬

[@grethstixx8078]

Chase Bowers some LED replacement lights have a red. White. And black color wires.

[@ChaseDaPlaya]

AmplifyDIY true but the 4 flat connector colors always mean the same thing so all you need to find out is what wire runs to what

[@user-ih2cc2wg2g]

The wiring I bought has two plugs, a male and female. Does a standard utility trailer have a plug somewhere in the frame? Very nice wiring video...

[@sonny62denali]

My wired drag the floor now sometimes it works sometimes it don't and it's bend it do you think that I'll mess it up I have to do the same thing you did I believe I also have the 4-way flat pin

[@AmplifyDIY]

Yeah, sounds like you need to replace the harness, just as I did in this video. Good luck!

[@polkadotz666]

Thanks for the video. The best price I could find on getting the pigtail part similar to yours here was buying an extender off Amazon and cutting off and installing the part I needed to replace…vehicle end. So I did everything exactly to your instructions with solder and heat tape and when I checked to see how it went I got no active lights on the trailer. Luckily I have two trailers so I tried them both and neither worked. So I undid everything, re-cut and strip the wires, and just twisted the new wiring together to retest and still nothing. Any idea what could be wrong? My old part was destroyed dragging the road but worked fine just a couple weeks ago.

[@AmplifyDIY]

Hi Collin - apologies for the late response. Hopefully you have figured your connector out - but if not: have you tried to do a continuity test on the wiring of the trailer *before* adding the pigtail? When stuff does not work right, I like to take a step back and start troubleshooting at the beginning. I'd start by doing continuity checks on each of the pigtail connectors and their wires, and then each of the trailer wires on the trailer. I'll bet you'll find something not connected/working with that testing.

[@Rokynutz]

Everything was great on the soldering. But, those safety chains(pretty much with any 🪝), under hook them.

[@Rokynutz]

Awesome, straightforward video regardless.

[@AmplifyDIY]

Great tip on the chains. Thanks for watching!

[@minihypehouse5624]

I have 8 wires how do I do it?

[@TheGregWallace]

Comment......you should hook your chains from underneath so if you hit a bump your chains will not fall off and you should also cross your chains. Crossing your chains makes a basket so if your trailer hitch comes off the ball the chains will catch it and keep it from dragging the ground. Also twist your chains to take some slack out if need be so the chains will not drag the ground.

[@AmplifyDIY]

Great tips - thanks, Greg!

[@dunerinaz]

So funny I find this video. I'm here because I lent my trailer to a neighbor and didn't realize until yesterday when I needed it that the connector was snapped in half and could tell it was dragging the ground. I showed him and I only got "oh wow, had no idea. Will it be hard for you to fix? I'll be sure to remember that next time" That's when I asked him when he was buying his own trailer.

[@AmplifyDIY]

Yeah, I was taught at an early age that when you borrow something you return it in exactly the same condition (or better) than when you picked it up. If anything gets damaged, you take care of repair/replacement to make it right. Unfortunately, not everyone feels the same way, it seems. Best of luck getting your trailer repaired... I'm happy to try to answer any questions that may come up for you. Good luck!

[@01hondascott]

I'm about to fix mine as well, i lent mine out for the whole winter last year to my brother in law to go snowmobiling, this year it needed a new deck, new leaf springs, and i noticed the ground wire was ripped out of the plug. I don't think ill be lending it out again.

[@AmplifyDIY]

@@01hondascott Oof. Really stinks when people don't take care of borrowed items. Best of luck getting it all fixed up!

[@01hondascott]

@@AmplifyDIY Thanks buddy, and you are right it does suck, especially where my bro in law is the type of guy that has to keep all his stuff pristine and won't even lend his stuff because something might happen to it, I never imagined he would treat my stuff that way. I guess is was a teachable moment.

[@warrenlouisiana2277]

Yep % 100

[@titchglover2601]

Can I use the same solder that I use for plumbing copper?

[@titchglover2601]

answer is no nvm

[@AmplifyDIY]

They use different kinds of flux. Plumbing solder uses an acid-based flux which can make for weak electrical connections: fastenerengineering.com/whats-the-difference-between-electrical-solder-and-copper-plumbing-solder/

[@christopher01221]

My trailer plug has 3 white, 3 brown, 1 green and 1 white wires. Don’t know how to tackle this

[@evana4752]

Would it be OK to use wire nuts and electrical tape in place of soldering and heat shrink? Don't have the equipment and trailer will be stored inside when not in use.

[@AmplifyDIY]

Hi Evan - you *really* should not use wire nuts and tape on these connections. They need to be able to hold up to inclement weather while you are driving, as well as tons of vibrations etc. A cheap soldering iron that can do the job can be had on Amazon for around $20. Here are links to the resources I used in this video: Inexpensive Soldering Iron: amzn.to/33hOd5I Assorted Heat Shrink Tubing: amzn.to/2rfb5oj Trailer Wiring Harness: amzn.to/2PJz0Gq

[@RRCCreative]

Can I use electrical tape instead of solder and heat shrink casing ?

[@AmplifyDIY]

Hi Matt - you really should solder the connections. Some wires just twisted together and taped up will not last long, due to the vibrations etc inherent in a moving vehicle. Good luck!

[@JasonWjddphotography]

Is it any big deal if I want to splice the other side, on to replace my corroded one on my truck? As long as the truck is off, should be ok? trailer side is fine.

[@AmplifyDIY]

Hi Jason - the technique I showed applies to both the trailer pigtail and the truck connector. Yes, keep the truck off, and make sure you are connecting the wires up in the right order. The wiring colors may not match, so I recommend you try to get a picture of which color wire from the truck goes to which connector on the plug before you even cut anything apart. Good luck!

[@MrTaylorfenoglio]

Someone was a little upset with their friends lol

[@AmplifyDIY]

Let’s just say we’re more careful about who borrows that trailer....

[@MrTaylorfenoglio]

@@AmplifyDIY ha ha I get it

[@aprendiendojuntosconJP]

I hooked the yellow and brown to the driver side for my trailer. I hooked the brown and green to the passenger side but the light does not turn on it just gets hot. If anyone can helo i would appreciate it.

[@AmplifyDIY]

Hmm... if it just gets hot, there is a short to ground somewhere. You'll need to check all the wiring along the frame of the trailer to see where the insulation has worn through so that the conductor of the wire is touching the frame of the trailer. These are hard to find - good luck!

[@aprendiendojuntosconJP]

Thanks

[@jaredwiman1845]

My trailer has a 4 flat with 5 wires going into it, one just grounds off to the tounge, I can't find a new harness with 4 pins and 5 wires how do I need to connect them to just use the 4

[@AmplifyDIY]

Hi Jared - after a bit of banging around on google, I found this question and answer from etrailer that I think will address your question. I've ordered stuff from etrailer before (hitches, adapters, etc) and have always found their information to be spot on: www.etrailer.com/question-363568.html Good Luck!

[@noneofyourbusiness8092]

Some don't give two shits about tearing up things, if it's not about them.

[@CHIPPOFISHING]

lighter to melt insulation

[@AmplifyDIY]

Yeah, use a heat gun. Much safer.

[@CHIPPOFISHING]

I would think a heat gun would be unproductive to remove a wire insulation on a single wire beside other wires. I actually suggested using a lighter to remove wire coating on thin wire instead off messing up with wire stripping on 14 gauge

[@mknight6026]

If you cut each wire a tad shorter then the first then you wouldn't need all them shrink tubes keeping the wire the same diameter throughout.

[@AmplifyDIY]

Great tip!

[@mknight6026]

@@AmplifyDIY Also something I have never done is add silicone grease to the wire before shrink tubing but I'm going to start doing that since I live on the coast and the air is salty here. Can't hurt

[@AmplifyDIY]

That’s also a great idea. You may also want to try he heat shrink that comes with hot glue inside it. That will also make a water-tight seal. Good luck!

[@mknight6026]

@@AmplifyDIY I didn't know that was a thing thanks

[@DonnieDarko727]

Music?

[@AmplifyDIY]

Hi Donnie - Music used in this video: "Wishful Thinking" by Dan Lebowitz "Michigan Greens" by Dan Lebowitz "Jeremiah's Song" by Dan Lebowitz "Glen Canyon" by Dan Lebowitz "Firefly" by Chris Haugen Thanks for watching!

[@marte1a256]

Mine seems to have five wires but no breaks is that fifth wire maybe a ground every plug I find is four wire and the truck is four wires

[@AmplifyDIY]

Hi Marte - a 5 wire connector usually is for a trailer with brakes. It's possible that whoever wired your trailer simply used the wrong connector, and left the brake wire disconnected.

[@marte1a256]

@@AmplifyDIY no I figured it out. There are two brown wires which go to each side as ground. So I put them both into one connector attached to the green wire on the plugThank you for replying though a lot of people don’t even do that

[@TheGregWallace]

Comment......This is why you don't let your friends and neighbors borrow your trailer.

[@billy-bo-dilly]

The only suggestion that I have is to ladder or stagger the four splices rather than placing them all in the same location. That will keep you from having an egg in your harness.

[@AmplifyDIY]

That's a great suggestion - thanks! And thanks for watching!

[@dcreno]

Soldering tips: First, buy solder "flux" when you buy the solder and put that on the exposed wire before soldering. Second, use the soldering iron to heat the wires and touch the solder only to the wires, never the iron tip. This ensures that you don't have a "cold joint" which is weak. Very clearly shown here: kzbin.info/www/bejne/p6nUi31-aLiZhJY

[@AmplifyDIY]

Good tips, thanks!

[@BillSias-op7xw]

I suppose when you went to school, the instructor played music while giving the instruction! EVER THINK THAT IS ANNOYING?

[@AmplifyDIY]

Hi Bill - apologies that the music was distracting. I appreciate the feedback and will keep that in mind for future videos. Thanks for watching!

[@brentbradley6711]

@@AmplifyDIY Music is never good for any video.

[@SozoSeasonFreedom]

​@@brentbradley6711Are you new to the internet? 😄

[@eddiemartinez4060]

You forgot to mention don't loan out your trailer that's the easiest fix

[@AmplifyDIY]

An ounce of prevention is worth a pound of cure, for sure.

[@urielgarcia6936]

I have all the wires only difference is mine has 2 brown wires what’s the difference

[@AmplifyDIY]

Likely your trailer or vehicle harness just used different colors. You'll want to trace where each wire goes.

[@eddiemartinez4060]

Now it's all fixed to loan it out again buy another connector 😂😂😂😂😂😂 just don't loan it out that's something you left out

[@stephenwhiting9611]

Challenging the notion that there is no such thing as a stupid question: How do you keep yourself from being electrocuted? I can't seem to figure out how to disconnect the end that is currently hooked into my car?

[@AmplifyDIY]

Hi Stephen - the only stupid question is one that is not asked. First off, the term "electrocution" means that someone dies as a result of an electric shock. Your car's electrical system is simply not strong enough to electrocute you... though it is possible that it may shock you. However, since it's only a 12 volt system, and the natural resistance of your skin is actually pretty good, even if you walked up and touched both the negative and positive terminals of the battery in your car at the same time, it would not be dangerous. You'd likely feel a tingle, but the scenes in movies of people being tortured with leads connected to a car battery is more or less completely overdramatic movie effects. As for how to disconnect the end that is connected to your car: do you mean that you need to remove the receptacle that is wired into your vehicle? Or do you mean you can't figure out how to disconnect the plug that goes to the trailer from your car?

[@stephenwhiting9611]

@@AmplifyDIY Thank you! I am wondering how to disconnect the receptacle that is wired to the car.

[@AmplifyDIY]

@@stephenwhiting9611 That receptacle is typically wired into one of the rear tail lights of the vehicle. Are you hoping to completely remove it, or just repair the receptacle? If you give me some more details (some pictures would be really helpful) I'd likely be able to provide some better advice. Feel free to email me directly: amplifydiy (at) gmail (dot) com.

[@djordan7979]

I'm sorry but you did all that work to cover the wiring with two sizes of heat shrink tubing... But you left the last 8 inches near the plug exposed? That doesn't make a bit of sense. Lol why not cover all of the wiring?

[@AmplifyDIY]

Heh - great point! I didn't have any more of the larger heat shrink on hand. It's 2 years later now, and the trailer wiring is holding up fine (this trailer gets used quite often). Thanks for watching!