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35 Ft 4-Way Trailer Wiring Harness - Wishbone Style - 42" Ground
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35 Ft 4-Way Trailer Wiring Harness - Wishbone Style - 42" Ground

Item # A35W42B
Our Price: $20.96
You Save: 18%
Trailer Wiring
Shipping Weight: 1.19 lbs
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4-Way trailer harness connects to your tow vehicle to control trailer light functions. Wishbone-style harness comes with 2 tail light wires split for simple wiring. Great Prices for the best trailer wiring from Optronics. 35 Ft 4-Way Trailer Wiring Harness - Wishbone Style - 42" Ground part number A35W42B can be ordered online at or call 1-800-940-8924 for expert service.
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Optronics Trailer Wiring - A35W42B

  • Trailer Connectors
  • Trailer End Connector
  • 4 Flat
  • Plug and Lead
  • 31 Feet and Longer
  • Optronics

4-Way trailer harness connects to your tow vehicle to control trailer light functions. Wishbone-style harness comes with 2 tail light wires split for simple wiring.


  • 4-Way trailer harness connects to your tow vehicle to control trailer light functions
  • Wishbone-style harness comes with 2 tail light wires split for simple wiring
    • Allows you to run wires separately down each side of the trailer to tail lights without needing a jumper wire
  • Color coded wires help with installation
    • White - ground
    • Brown - tail lights
    • Yellow - driver side stop/turn
    • Green - passenger side stop/turn


  • Wire harness length: 35'
  • Ground wire length: 42"
  • 3-Year Warranty

Manufacturer Cross Reference
Harness will work as an exact replacement for:

  • Truck Lite # 108835
Wishbone Wiring Diagram

A35W42B Optronics 35 ft. Wishbone 4-Way Trailer Wiring Harness with 42" Ground Wire

Alternate part number: A-35W42B

California residents: click here

Customer Satisfaction Score:

Customer Reviews

35 Ft 4-Way Trailer Wiring Harness - Wishbone Style - 42" Ground - A35W42B

Average Customer Rating:  4.8 out of 5 stars   (739 Customer Reviews)

4-Way trailer harness connects to your tow vehicle to control trailer light functions. Wishbone-style harness comes with 2 tail light wires split for simple wiring.


2 things. 1st@: I think there should be an option to pick tinned wire. 2nd: The ring terminal for the ground needs to be bigger.


Worked out great. Direct replacement for my old 4-way boat trailer harness that had corrosion damage at a quick splice joint causing my trailer marker lights to not work. Easy to follow wiring diagram from etrailer store page.


Great product very easy to install my order arrived 3 days early I received emails so I was informed when my wiring harness was shipped and one when it was delivered Thanks E Trailer A happy customer!!!


A quality wiring harness, plenty long enough for my boat trailer.


1 year, and so far so good. I have had cheap harnesses before that would oxidise from the inside out and break when connecting flat 4, but this one is doing fine.


Good wishbone wiring harness, decent ground eyelet, not tiny


Replaced the wiring and lights on my 1992 boat trailer. I was able to get everything needed from etrailer. I think Optronics is of the highest quality
and recommend both etrailer and Optronics product.


I want to thank you for all your help with my trailer you were more helpful than you realize. So this is my trailer for a 22' Flats Cat shallow draft Catamaran. I totally dismantled my trailer and buffed by hand with a wire buffer and sand blasted in some spots and applied multiple coats of some very expensive galvanize paint (Z.R.C.). I installed all new C. E. Smith Carpet (about 80'), seven new LED waterproof lights, new springs, new equalizers, new tongue jack, new wench, new safety chain, new chain brackets, all new SS hardware and a 35' long wiring harness.
I was able to send only one review with a picture of the safety chain and brackets. I'm having a little trouble with the rest..oh some of these items were bought locally or from your competitors, until I found ETRAILER. Your prices were cheaper for the exact same things. Your helpful how to videos were helpful. And Rose, your personal helpful knowledge made my buying experience very pleasant, I actually enjoyed talking to you! Thanks to ETRAILER and specifically to Rose G.


The white wire needed to be a bit longer, but I made it work, other than that a


The wiring harness arrived quickly and was installed with ease.


The plug looks and feels solid! This is the only place that had a long enough wiring harness to do what I needed. Shipping was also very fast!



After one year, It is still working great! It makes all the difference having long enough wires to where there is no splicing on a saltwater boat trailer.


I am giving this item an Excellent review based on my former (very positive) experience with your products, but actually I haven't used it yet. My former harness is still working. I will use this as a replacement when the time comes.


Perfect! Just what I needed!!
I could
only find a harness plug with one brown wire (4 wires total) at my local stores. I "googled" the problem I had (my harness plug had 2 brown wires). A rep from etrailer had answered someone's same question on a message board. It was a detailed explanation as to why one would need this part. Then the rep put a link to the etrailer site. And there is was, the harness plug with 2 brown wires (5 wires total) and at an agreeable price to boot!!!!! And now I know about the etrailer website!!!!


High quality, fairly priced, totally sa tisfied!


This harness is exactly what you expect to receive when you order it.


Item was exactly as described and just what I needed to rewire my trailer. I also appreciate the great customer service as I was emailed instructions to aid me in the installation of the item ordered.


This worked great, had to rewire my trailer after having it painted and reconfigured and this item was long enough and allowed me to tie in my additional lights.


When it was time to rewire our 2007 boat trailer I selected the wiring harness from etrailer because of its wishbone configuration, long ground wire and quality. We used an electrical fishing tape to pull the wire through the channels of the trailer and it was straight forward and relatively easy. It has worked just fine and we have no complaints. Great price and fast service too.


A basic wiring harness, meets its purpose very well. Arrived on time.


This harness has a heavier gawg than the box store brands. Rseems to be good quality.


Rewired trailer lights. Solid product. After 1 year no issues noted.


Absolutely Fabulous! Exactly what I was looking for but couldn't find at any retail store in my area! The wishbone design splits the brown wire at the plug. Makes wiring both sides of the trailer with no splices or having to find additional brown wire sold by the foot!


Exactly what I needed to rewrire my boat trailer. Received sooner than expected as well.


Very pleased with products and service . Both items I purchased for my new trailer I built. I needed a coupler that would fit into the 4x4x1/4 in tubing and etrailer came thru with a perfect fit at a great price. My trailer is 28’ long so the standard 25’ harness oils not work. Again etrailer came thru with a 35’ harness which is what I needed. Both these items were shipped quickly and at a great price.


Typical style wire. Not that you really need it but no diagram came with the wiring as it shows on the website. Would be helpful tho

Etrailer Expert

Katrina B.


This harness is a wishbone style, which is where the browngreen wire for the running lights are on the right side and for the left side running lights, a yellowbrown wire. The yellow wire is for the turn signal and brake lights on the left side. The green wire is for the right side turn signal and brake lights. Finally, the white wire is for ground. I will email you the wiring diagram so that you have a better visual.

Show More Reviews

See what our Experts say about this Optronics Trailer Wiring

  • 40' Wishbone Trailer Wiring With A Ground Wire Running Down Both Sides
    We do not offer wishbone wiring that has a ground wire going down both sides. You really don't need it because the ground wire is for the plug itself not the lights and you want the ground close to the plug. I recommend using the 4-Way Wishbone Trailer Wiring Harness Item # A40W42B.
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  • Can Trailer Brake Magnet Wiring that is Red be Ran to Wiring that is Yellow
    The great thing about trailer brake magnet wiring is that the wiring isn't polarity specific. That means that either wire can be used as power or ground as long as opposite wire is connected properly. So it doesn't matter which wire you run to your magnet wire by color as long as the other wire is connected properly.
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  • Running Light and Reverse Light Circuit Not Active on Ford F-150
    It sounds like you have narrowed down the issue to the truck considering you do not have the same issues when hooked up to another tow vehicle. The first thing you want to check is the ground on the 7-way of the truck to make sure it is properly grounded to a clean bare metal surface on the truck's frame. I am assuming the actuator on the trailer has an electric lockout that allows you to back up with hydraulic brakes. For the electric lock out to function properly, you need a working...
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  • Is Optronics Trailer Wiring Harness # A35W42B Copper Core or Copper Clad Aluminum
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  • 4-Way Trailer Recommendation for Trailer to Replace Wrong Style Connector on Trailer
    Sounds like somebody installed a vehicle side 4-way on your trailer's wiring. While there isn't an adapter I can offer you the best solution would be to cut the 4-way off of the trailer and then wire in the part # A35W42B.
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  • How to Install New Tail Lights with Different Color Wires
    There is not a standard wire color to function chart on a trailer for anyone to abide by so it will be best to test for function with a circuit tester. In order to check this all you need to do is start the vehicle, plug the trailer connector in, and test each of the wires while the corresponding signal is activated. The light should then specify which wire is for which function but you will again need to test the trailer wiring to determine which color wire has which function. Unfortunately,...
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  • Trailer Brake Wiring for Tandem Axle Brake System
    I'm not sure what the sensor you describe is for. Typically trailer wiring is color coded so that right turn and brake light signal is carried by a green wire, and the brown wire carries the running light circuit. The brake output circuit is usually carried by a blue wire which travels to each brake magnet, where it attaches to one lead from each magnet. The other lead from each magnet will ground to the trailer frame. I'll give you a link to a typical trailer wiring diagram. I also...
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  • Wiring Electric Trailer Brakes with Magnets that Have 2 White Wires
    It sounds like the magnets or their wiring could be bad. Your 2012 Chevy Silverado 2500HD is probably sensing the wrong resistance from the trailer brake magnets and that is why you see that warning message. When magnets have 2 of the same color wire it usually means that you can use either one for either function. The black wire with the 12 volt power should not be attached to the brakes. Only the blue wire should connect to the brakes. The other magnet wire should be attached to the...
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  • Where Does Red Wire of 4-Way # 62990 Wire To on Trailer
    While we do not carry the 4-way kit part number 62990 I can tell you how it wires up. Basically the harness is a wishbone 4-way which has two wires for the running light circuit. One for each side of the trailer. The red wire goes to one side of the trailer's running lights and the brown goes to the other. Doesn't matter which side you pick. We have a similar wishboned 4-way wiring harness as part # A35W42B.
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  • Determining What 4 Wires that Run to Trailer Hub are For
    You'll probably have to pull off the hub/drums to see where the wires go. It's most likely that your assemblies have two magnets and two of the wires are power and two are ground, one for each magnet, but since your configurations is not standard we'll have to look further into what's going on with the assemblies. Can you get me pictures possibly of the magnets? If you see two wires ran to each magnet you'll need to run a power circuit and a ground to each of them since they are not polarity...
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  • Tracking Down Possible Poor Ground Connection on Travel Trailer
    What you're describing is the classic symptom of a poor ground connection somewhere in your trailer lighting system. When all the functions are being used, you're drawing maximum amperage through the system, which is when a ground problem will manifest itself. Trace the white ground wire back from the trailer connector. The wire will usually ground to the trailer frame somewhere on the trailer tongue. Make sure this connection is secure and not corroded. Each trailer lamp will also have...
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  • Gauge of Wiring in 35 Ft 4-Way Trailer Wiring Harness # A35W42B
    The gauge of the wiring in the 4-way kit part # A35W42B is 18 gauge.
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  • Installing 4-Way Connector on Trailer with 5 Wires
    If you have 5 wires on your trailer and a 4-pin connector, you most likely had what is called a wishbone harness on the trailer like # A35W42B. On a wishbone harness, you will have two wires attached to the running light circuit because there is one wire for each side of the trailer. I recommend testing the wires on your trailer with a 12V battery so you can verify each of their functions. Going by color alone is not the best method, as manufacturers and aftermarket wiring can change...
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  • Is the Optronics 35 Ft 4-Way Trailer Wiring Harness Wire 100 Percent Copper
    I reached out to Optronics and they confirmed that the wire used in the 35 Ft 4-Way Trailer Wiring Harness - Wishbone Style # A35W42B is 100% copper. This harness comes with 2 tail light wires split for simple wiring and has a 3 year warranty.
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  • Wiring Stop Turn and Tail Light Circuits to a Trailer Light
    Your trailer lights should only have one wire if the light serves only one function (tail light, marker light, stop/turn). The white wire shown in the photo that you attached is a ground wire and will not be connected to the tail light or stop/turn circuits. The bulb attached to your light housing looks like an 1157 bulb, which is a dual filament bulb that has two contacts for two different circuits. You should have two wires on the back of the light housing, one for the stop/turn circuit...
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  • Troubleshooting Trailer with LED Taillights Where all Lights Shut Off When Running Lights are On
    I'd be willing to bet you have a short on the running light circuit of your trailer wiring that's touching the trailer frame which is causing your problems. Since the lights are grounding through the frame a short to the ground of all of the circuits will take out all of the lights that are using the frame as a ground. Go over the running light circuit looking for any cut or exposed wire and fix as needed.
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  • Troubleshooting Dim Blinking on Left Turn Signal When Right Turn Signal On
    More than likely this is a short in the trailer wiring or corrosion on your connector. Go ahead and inspect your connector on the trailer and vehicle side. If any corrosion is present, it is possible power is moving over causing both to run at the same time. One way or another it would be a good idea to clean both. After you check the connectors, go ahead and make sure your ground wire is secure. This is an easy thing to check and the source of many problems. Assuming your ground is in...
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  • Troubleshooting Trailer Brakes that Lock Up When Connected to Junction Box
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  • All Trailer Lights Blink With Turn Signal on 2007 Triton ATV Trailer
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  • Trailer Lights are Dim When Connected to Truck
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  • What Wire Gauge is Used on the 35 ft. Wishbone 4-Way Trailer Wiring Harness, # A35W42B
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  • Troubleshooting Trailer Wiring Brake Circuit Signal that Stopped Working After 7-Way Replacement
    Since the trailer is no longer able to recognize a trailer connection the issue is most likely that the brake output circuit of the wiring was damaged when the old one was yanked out. This is a fairly common issue so you'll need to go over the wiring looking for any shorts or broken wire and fix as needed.
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  • Wiring Brakes On Tandem Axle Trailer
    Typically trailer wiring is color coded. The brake circuit is usually a blue wire which travels to each brake magnet, where it is attached to one wire from each brake magnet. The other wire from each brake magnet will ground to the trailer frame. I have attached a drawing that shows how the wiring is typically run for brakes on a trailer. I have also attached a link to trailer wiring diagrams that may help.
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  • Troubleshooting Trailer Running Light Circuit that Turns Off When Interior Lights are Turned On
    Your problem is due to your trailer wiring ground circuit being insufficient. Basically you are trying to draw more amperage than you ground circuit is capable of keeping up with so it's shutting down partially. Since the interior lights and running lights are on separate circuit it wouldn't be an overdrawing of either circuit so it's definitely a weak ground. So you need to improve the ground of the trailer wiring. You can do this by running jumper wires from the circuits back to the...
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