Troubleshooting Blown Vehicle Fuses Every Time Trailer is Connected

Question

Question:

I keep blowing fuses on my truck when I plug my trailer in. The turn signals and brake lights will still work but no running lights

asked by: Joseph S

0

Expert Reply:

It sounds like there is a short somewhere along the wiring of your vehicle or trailer that is causing a fuse to blow every time you connect.

The first thing I recommend doing is disconnecting the trailer and using a circuit tester like # PTW2993 to test the vehicle side connector. You can have a buddy run through the functions from inside the vehicle while you test each pin on the connector. If you detect any power to a circuit when there should not be any, then you know there is a short somewhere on the vehicle side. Simply trace along the wiring and look for any exposed areas that might be touching bare metal.

Also check that both the vehicle side and trailer side connectors are free of dirt and corrosion. If the connector is corroded or dirty, it can cause excess power draw and blow a fuse. Simply clean out as needed.

If everything checks out fine on the vehicle side, then you will want to check along the wiring for the trailer, again looking for any damaged or exposed wiring. You can also test the trailer wiring for function by connecting each wire to a 12V battery. Lastly, make sure that the main trailer connector ground and all the light grounds are securely attached to clean bare metal surfaces.

If you are unable to find the issue, please let me know and I will be happy to look into this further.

expert reply by: Chris R

0

Ge

3/25/2020

Good morning my trailer battery fuse keeps blowing any suggestions where I can look?

Reply

Chris R.

3/25/2020

Are you using that 12V circuit from the 7-Way to do anything other than maintain the charge on your trailer's battery (hooking up a jack or winch, etc)? If not, then the most likely cause is a short somewhere on that particular wire. If you're able, try inspecting the 12V wire up the truck from the 7-way and look for any exposed or pinched areas that need to be fixed. Also look at the 7-Way itself to see if there is any corrosion or debris built up inside the pins that needs to be cleaned out. Let me know what you find and we'll go from there.

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Nick

12/20/2024

@ChrisR Hey Chris. I'm having a similar issue as this gentleman was. We just purchased a new enclosed trailer and it keeps blowing the 30 amp trailer battery fuse in my truck's fuse box. The only thing I've identified that the 12v out of the truck powers is the interior lights. Is this common and could that be my issue? 2019 Chevy 2500 7 Pin connector

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Robin H.

12/20/2024

@Nick I'm sure the lights are pulling too much power for that circuit to handle which is why the fuse keeps blowing. I would add a battery like # BRW34FR to the trailer to power the lights. The 7-way will act as a maintenance charge but won't actually charge the battery so you will either want a battery charger like # 329-GENIUS5 to charge it when you have AC power or you could add the # 331-BCDC1225D to your Silverado to charge the battery using the truck

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Andrew F.

5/12/2020

Good afternoon, I recently replaced my 4-pin on my boat trailer. The original 4-pin on it had 7 wires going to it. 1-yellow, 1-green, 2-brown, 3-whites. The new 4-pin only has 4 wires, yellow, green, brown, white. When I spliced them together, I put each color together (therefore there were 3 white wires I spliced to the 1 white wire on the connector and 2 browns to the 1 brown on the connector). When I plugged it in, it all worked but by the time I got my boat to storage and unplugged then replugged it in, I noticed the lights didn't work anymore. Turns out I blew 2-20amp fuses. I wanted to inquire if this could have been caused by my splicings of the different colored wires touching (at the time, they weren't heat shrinked and could have touched the other exposed wires I spliced together in transit to storage), or if it could be overloading the ground wires having 4 wires all connected? Thank you for your assistance.

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Chris R.

5/14/2020

Exposed wires coming into contact with each other could definitely do it. This would have cause a short and a sudden bolt of power on whatever circuits were involved. I would definitely clean those connections up as soon as possible and hopefully it resolves the issue, but if not let me know!

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Beto R.

7/7/2024

@ChrisR Hola tengo una ram 2022 3500 apenas me enpeso a quemar el fusible de las luces de mi traila cuando le pongo nuevo el fusible si prenden las luces de la traila pero muy bajita y luego se funde. direccionales luces de emerjensia frenos todo le sirve nomas se funde el fusible de los cuartos o (luces) del remolque que podra ser?

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Kevin C.

7/8/2024

@BetoR If the fuse is blowing and the lights are dim then you either have the incorrect sized fuse for the circuit or you have a damage somewhere in the wiring and it's touching metal causing a short. You'll want to trace the wiring for damage, check the ground for loose or corroded connection, and check that you have the appropriate sized fuse for the lights installed.

Reply

Herman

9/20/2024

It all started when I pulled away with out unplugging my electric jack on my trailer. I was using my 7 pin trailer plug on my pickup and put one on my electric jack for powering up my jack. Bought a new plug and installed it. So when I went to hooked up my trailer and my ball and trailer hitch touched it sparked and blew a 40 amp fuse. But when I hook up my trailer all lights work fine. Please help.

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David H.

9/28/2024

I installed a hopkins 4 flat kit #43425 (that I bought from etrailer) and it tested fine. I didn't have my trailer yet but when I went to pick it up and connect the lights, they didn't work. Blown fuse. Why would the fuse blow before I ever hooked up a trailer? I'm going to replace the fuse and try again but I wanted to get ahead of the problem in case it continues to happen. The vehicle lights are working fine and there was no trailer hooked up so the problem must be in the converter box or harness wires, right?

Reply

Chris R.

9/29/2024

@DavidH Hey David, that's definitely strange. Are you sure the fuse blew before you hooked up the trailer? Or is it possible it happened right when connecting. There could be an issue on the trailer side that's causing the fuse to pop when hooking up, such as some exposed wiring.

Reply

David

9/30/2024

@ChrisR Good morning Chris. Thanks for the prompt response(I'm impressed)! Yesterday, the fuse blew with the trailer hooked up. When I read your email, I went out and replaced the fuse without the trailer hooked up and tested both sided of the fuse. All good. Tested the 4 pole, good. Hooked up the trailer and all the lights are beautiful. I'm good for now and hopefully, it won't happen again. Since I didn't actually find the problem, is there anything that I can do to minimize the possibility of repeatedly blowing that fuse?

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David

11/2/2024

@ChrisR The trailer is not connected so it can't be on that side. I've checked the insulation on every wire on both sides of the converter box. When I try to put a fuse into the power line, it blows up instantly before I can let go of it.

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See All (5) Replies to David H. ∨

David

9/30/2024

My trailer is new and Tractor Supply has been excellent to work with. They have assured me that if my problem is discovered to be on the trailer side, they will repair or replace whatever is necessary. My vehicle is very old (2003 Highlander/300K+ miles) and is known to have electrical issues. Specifically, where should I apply the grease that was in the wire harness kit. I'm willing to buy more grease if necessary to avoid future trailer light problems. Would electrical tape help? Are there common weak points in the system that tend to be problematic? Any preventative maintenance that you could recommend would be appreciated. This is my FIRST trailer

Reply

Chris R.

10/1/2024

@David That's a fun first experience. Hopefully you're good to go now. Trailer wiring/lights are weird sometimes....it could have been a lot of things that caused a sudden surge of power. As for the grease, you'll just want to apply some to the actual pins/terminals of the 4-Way connector before hooking it up to the trailer's. This will prevent rust and corrosion from building up over time.

Reply

Matt

11/28/2024

My turn signal fuses (10 amp) on the 2019 Silverado both (left and right) when I connect to the trailer. It is a 4 prong hitch. Any idea why both would blow. The running light (30 amp) and brake fuse (20 amp) do not blow. Thanks

Reply

Bryce D.

11/29/2024

@Matt Since it blows when connected to a trailer that would mean there is a short somewhere on that circuit. You're going to need to do a little bit of wire hunting to look for that short and repair it. You'll want to look out for broken or frayed wires, any pinches, or corrosion on connections that are jumping between circuits. It also wouldn't hurt to check your connectors for any rust or damage as well as making sure the rest of your wiring is good.

Reply

Caleb A.

8/29/2025

Hey Chris I’m having the same Issues just recently started and I pull my trailer everyday for the past 2 years and now every time I change the 2 fuses in my box on my truck (one is the running lights and not sure what the Other is for) and crank the truck after a few seconds or sometimes it’s takes a hour but before long they blow agin and I’ve looked everything over not the greatest inspection but got under truck and trailer and didn’t find anything bout to go buy a tester now but it’s hard to find the time to Shut it down this time of year but I use it for my business and leave the house at like 3am so need my running lights bad. My brake lights and turn signals work just not the running light. Also noticed the other day something have drained my battery just once so far. I jumped it with my jump box and had been fine sense also had a blow out around the time this started I think could the wires running to the trailer brakes be the issue

Reply

Chris R.

9/2/2025

@CalebA Hey Caleb, that sounds like a frustrating nightmare. Something is definitely shorting out on the trailer wiring. That's a lot easier to say than to actually find and fix, though. My money is on a bare piece of wire (along the running light circuit) touching the frame somewhere. You mentioned doing a quick inspection, but I'd definitely try and do a full, thorough inspection along the whole trailer (specifically that running light wire). The other potential option is to simply cut that circuit off at both 7-ways (truck and trailer) and run a new wire to simply bypass the faulty circuit altogether.

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