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Brophy Circuit Tester for 4-Pole Flat Trailer Connector

Brophy Circuit Tester for 4-Pole Flat Trailer Connector

Item # F4CT
Our Price: $16.23
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Circuit tester plugs into your 4-way flat trailer wiring harness and identifies lighting problems. Labeled LED lights illuminate to show which functions are working properly. 1-833-496-1390 to order Brophy electrical tools part number F4CT or order online at Free expert support on all Brophy products. Great prices and Fastest Shipping for Brophy Circuit Tester for 4-Pole Flat Trailer Connector. Electrical Tools reviews from real customers.
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  • Reviews (156)
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  • Videos (2)
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  • Why etrailer?

Brophy Electrical Tools - F4CT

  • Testers
  • Tow Function Tester
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Circuit tester plugs into your 4-way flat trailer wiring harness and identifies lighting problems. Labeled LED lights illuminate to show which functions are working properly.


  • Circuit tester plugs into your trailer's wiring harness to check the conductivity of all the circuits between your vehicle and your trailer
    • Quickly identifies lighting problems
  • Labeled LED lights indicate which functions are working properly
    • Tail: tail lights
    • LT: left turn signal and brakes
    • RT: right turn signal and brakes

F4CT Brophy 4-Way Flat Circuit Tester

Video of Brophy Circuit Tester for 4-Pole Flat Trailer Connector

Videos are provided as a guide only. Refer to manufacturer installation instructions and specs for complete information.

Video Transcript for Brophy 4-Pole Flat Trailer Connector Circuit Tester Review

Hey there hollers. Today, we're going to be taking a look at Brophy's LED Circuit Tester. It's available in a 4-pole or 5-pole connection. Before you hit the road with your trailer, we always recommend testing things out to make sure it's working properly. One of the most important things to test out is the lighting so that others know your intentions around you while you're going down the road. Here at etrailer, we recommend testing your light at the source, which is your vehicle.

That's where this Brophy 4-Pole Flat Connector comes in, because when you plug in your trailer and you have a fault on your trailer, you're not going to necessarily know where the fault lies.With our Brophy 4-Pole tester we can eliminate the variable of our trailer and determine whether or not our vehicle side is working. We simply plug it into our 4-pole connection and then we can run through our functions. You'll want to make sure you have your left turn signal, your right turn signal, your tail lights and your brake lights. Now that you know that your vehicle's working properly, if there we're any problems with the lighting on your trailers end, you can isolate it just to your trailer, make those repairs, and then you're ready to hit the road. And that's going to complete our look at Brophy's LED Circuit Tester..

Customer Satisfaction Score:

Customer Reviews

Brophy Circuit Tester for 4-Pole Flat Trailer Connector - F4CT

Average Customer Rating:  4.9 out of 5 stars   (156 Customer Reviews)

Circuit tester plugs into your 4-way flat trailer wiring harness and identifies lighting problems. Labeled LED lights illuminate to show which functions are working properly.


This is a keeper everyone with a trailer wiring harness needs to purchase yes


Easy tester for trailer wiring harness. Made it easy to check as I installed new wiring harness and ran wires - to double check all worked before putting all the trim back in place.


Grounding issues are always a problem with trailer lighting (in my experience), and it is great that there is a product specifically intended to provide grounding continuity from the light itself to the tow vehicles wiring. Too many systems rely on a short pigtail attached directly to the trailer and a connection at the trailer ball.

I am hopeful that this will be a long-term solution.


This was a relatively simple and straightforward installation on my 2019 Volvo XC40. The directions were clear, although the black and white pics can be a bit hard to follow. I would add the following points. First, the left plastic rail in the spare tire compartment needs to be removed, and it has an odd hook at the front that is a challenge. It will come with some wiggling. It's equally challenging to put back on. Second, I used the Volvo ground terminal to ground the T-One module. Third, I ran the wire from the module to the positive terminal down through a grommet in the spare tire compartment, then along the brake lines under the car to the battery. This was easy to do with the vehicle on a hoist, but will be more challenging if you don't have access to a hoist. I removed 2 of the protective panels under the car to route the wire. It was fairly straightforward. The product works as advertised and fits very well in the car.


Products I ordered were delivered faster than expected with no issues. Keep up the great work. I would highly recommend this company. Install went great and according to on-line instructions on their website.


Worked great confirming the integrity of my trailer light install.


Overall a great product. Served it's purpose. Only reason I purchased was because I didn't have a trailer immediately available to test the electrical wiring I installed on the vehicle. If you have a trailer, I wouldn't bother spending the money on this, but for those like me that didn't have a trailer at the time, definitely a must-buy. Easy to use, and can help troubleshoot any issues you may have with your wiring.


While the product itself was excellent, the instructions were on the ambiguous side. Forget the instructions, and just watch the video to Hook Up----Suby's are so easy!!


Everything was as expected, wiring was plug n play and didn't take long at all to hook up ,
Thanks etrailer


Ordered hitch receiver with wiring for bike rack installation on 2019 Ford Explorer. Everything arrived in less than a week. Crawled under the car with my burly son and finished the installation in about an hour. Toughest part was getting the exhaust hangers off. Didn't have a tool for that. Online installation video was a big help. Hitch frame rubs against right side exhaust hanger, hence the four star rating instead of five. Exhaust still appears to be level and no weird noises, so not an issue. Get the little plug in light tester. It's worth it, then keep it in the glove box. Haven't purchased bike rack yet, but no concerns about the hitch.


A MUST have to validate a working system. Now when I rent a trailer and there is an issue with the lights, I will know it's the trailer and not my system.


This works just as promised and makes checking the wiring connectors much easier.


What is there to say about this. Easy to use, just plug it in, the LED lights are clearly marked. If your wiring is correct, the correct led lights will show.


Once I had the harness installed. It was great to plug the tester in and check my work. I would highly recommend this tool.

Well, Ive had this little tool for a year. Now I dont use it very much, but I recently noticed my trailer lights werent working when I plugged them into my truck. The tester helped troubleshoot the problem quickly and I was back in business. So again I work recommend buying this tool and keep it in your towing vehicle. You never know when it will come in handy.
Andrew - 09/06/2021


Well made and works well.


It's $4.82. worth every penny.


I bought this at the same time I bought a Hopkins Plug-in Simple Wiring Harness With 4-pole Connector. It worked exactly as advertised and let me test the wiring harness installation in advance of hooking up a trailer. Both products are excellent, and the folks at etrailer exceeded my expectations in all areas, particularly the very fast response to my order.

Still working great and very helpful to make sure all is well with the wiring harness in the truck. Definitely still recommend.
Chris - 04/16/2020


The circuit tester is just what you need to confirm the wiring harness you install was installed correctly the first time.


Great product,


Simple and easy to use


Totally transformed our 2017 Newmar Canyon Star ride. Best investment ever.


Worked great.


Perfect tool for testing the wiring. Narrowed it down to the trailer lights. Already order a kit from e-trailer.


Provides a quick way to check the tow vehicles wiring. Well worth the price.


This device makes testing the trailer wiring easy

Show More Reviews

See what our Experts say about this Brophy Electrical Tools

  • 4 Pole Circuit Tester Power Source
    The power source used to test the Brophy Circuit Tester for 4-Pole Flat Trailer Connector # F4CT in the referenced video I included is the Tekonsha Bench Tester # 7585. I've also included a review video for that product as well.
    view full answer...
  • Availability of Tester for 4-Pole Trailer Connector
    You bet we do! You'll need part # F4CT from CR Brophy. If you use the provided link, you can see a demonstration video.
    view full answer...
  • Will The Alpena Trailblaze LED Lights Interfere With The BLIS System On My 2018 Ford F-150
    I emailed Alpena to get some clarification on their Alpena Trailblaze Tailgate LED Lights, part # ALP77229. I was told that the placement of the LED lights will not block or interfere with the BLIS sensors. However, the newer model years of the Ford trucks, may think that a lightbar is really a trailer when they are hooked up to the 4-way connector due to the power draw of the lights. Alpena has not seen that be an issue with the Trailblaze Tailgate LED Lights, but the lights were launched...
    view full answer...
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  • No Right Stop/Turn Signals With T-One Harness 118525 On a 2015 Nissan Frontier
    It sounds like you are using some sort of plug-in LED tester like the Brophy Circuit Tester for 4-Pole Flat Trailer Connector part # F4CT and if that is the case then these are not always accurate and Tekonsha even recommends against using these, so you really need to do your testing with a incandescent circuit tester like the Draw-Tite Circuit Tester part # PTW2993. If you still do not get power on the right stop/turn circuit even with a standard circuit tester then be sure to give all...
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  • Troubleshooting No Runnings Lights After Optronics LED Combination Tail Light Kit Installation
    Thank you for purchasing the LED Combination Tail Light Kit for Trailers under 80" Wide # TLL9RK! To troubleshoot a certain light function on your trailer you definitely want to start off by checking your connections and grounds which is sounds like you've already done. After that the next step is determining which end of the wiring the issue lies on. To figure this out you can use a tester like the Brophy # F4CT on the vehicle side. For the trailer side you'll need to apply 12V power...
    view full answer...
  • Sporadic Lighting Functions for Trailer Lights on a 2017 Ford Edge
    For starters, the Curt T-Connector Vehicle Wiring Harness part # C56292 is for a 2017 Ford Edge with the Sport and Titanium package. If you have the SE and SEL package on your 2017 Ford Edge then you will want to use the Curt T-Connector Vehicle Wiring Harness part # C56272. With that being said an LED trailer connector tester like part # F4CT do not always work with all trailer wiring harnesses so this could be the issue. I would ensure that the circuits are working by testing them with...
    view full answer...
  • Can You Test the Curt T-Connector Vehicle Wiring Harness With a Volt Meter
    Yes, you can use a volt meter to test a trailer wiring harness like the Curt T-Connector Vehicle Wiring Harness. You'd simply be looking for around 12 volts on the circuit you have activated. The other ways we recommend testing are with a more basic test light like part # PTW2993 or plug in tester like part # F4CT. The harness don't read resistance on the circuit or anything so as long as you have power to the module box and the signal is activated in the vehicle then you will see power...
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  • Troubleshooting Always On Trailer Lights When Brake Controller Is In Use
    I would start by checking your 4-way connector, part # F4CT, and the 7-way connector part # PK12741. These wiring harnesses should be connected directly to the battery, not spliced into the wiring system. I would check this first. If everything is connected properly, I will start to troubleshoot on the vehicle side. Whether it is a problem with the ground, a short in the wire, or rust or corrosion at a connector. It appears that your vehicle's light circuit is always at continuous power...
    view full answer...
  • Right Turn Signal & Running Light No Working After Replacement
    We can resolve this issue. This seems like a 12-volt continuity to the lights, or a grounding issue at the lights themselves. Since you are having trouble with two different wires, but not all lights, I would double check your 12-volts to the right turn signal/brake light which is the green wire. I would also check the brown wire for the running lights. At the connector on the back of your vehicle check for 12 volts with your vehicle lights turned on. Then with the blinkers turned on....
    view full answer...

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Info for this part was:

Employee Lindsey S
Edited by:
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Employee Jeff D
Installed by:
Jeff D
Employee Dustin K
Installed by:
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Employee Chris R
Video Edited:
Chris R
Employee Amanda M
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Employee Jonathan Y
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