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

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

Item # A35W42B
Our Price: $12.16
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Trailer Wiring
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Shipping Weight: 1.17 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. Lowest 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 1-800-496-5010 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

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:  4.9 out of 5 stars   (656 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.


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.


I needed at least 28' of harness and most commercially available were only 20 or 25'. I really liked that this one was 35' to have some extra. Also liked the "wishbone" design as that is the easiest to use when wiring a trailer.


Fishing wires is always a hassle but your harnesses are fine.


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!!!!


My order always goes without a hitch… never an issue and shipping time is second to none!! Great service, great product! Will continue to use e trailer without a doubt.


Upon initial review, harness seems to be quality made.


Wiring harness is identical to the one on my trailer in need of repair. Price was good and shipping was fast.


Worked as described. Lots of extra wiring and very simple to install. Excellent pricing. Has worked well for the past year.


I ordered the 4 way trailer end plug/wiring assy (35 Ft 4-Way Trailer Wiring Harness - Wishbone Style - 42" Ground
Item # A35W42B), and it was at my house in about 3 days! And at a great price to boot!!

I checked around all of the local auto parts stores, and none even had this product on hand! I'm bypassing the local stores now when J can, and ordering strictly from etrailer. Their prices are great, product selection is beyond any others I've seen. And their professional and informed people never fail to follow up with a complimentary email to make sure everything is to my satisfaction.

If you're looking for towing-related items, look no farther than etrailer!!


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.


Nice harness plug is much nicer than your typical cheap wiring harness more along the lines of a wesbar.


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.


Order was shipped the very next day after placing it. E trailer sells reputable, quality products. I have always been pleased with the trailer related parts I have ordered.


Solved my electrical problem!


I ended up doing some metal work installed new leaf pins/bushing on that trailer, sandblasted, new paint/deck. so just installed about a month ago and works great . Quality wire should last. Thanks as always.


I have purchased twice for 2 separate boat trailers from etrailer. If you utilize a flat 4 plug as I do, they are a must. The harness coils nicely with ample extension. The harness is well built as is the majority I purchase from etrailer.


Works perfectly


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.
Eric - 01/29/2019


Website was very helpful as to finding the correct part numbers. My order processed and was shipped in great time! This is my first time dealing with this company, but not my last. I’m recommending to all of my family and friends!


I purchased this to update my very old and non-functioning pontoon trailer wiring. I needed the extra length and was glad etrailer provided it as an option. Since the new wiring harness was already set up to run each side separately, it made easy work of rewiring the trailer. I really like etrailer products. I think they are of good quality for a good price. Sorry, no photos of the job.

Working like a charm. Still happy with the product and the outcome.
Lauri - 05/18/2021


That order was placed months ago, way beyond my ability to remember any details.


Like the "y" design. I have rewired alot of trailers and really made it simpler


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!


Awesome service

All great and awesome service
Danny - 07/23/2022


I recently bought a 2004 Trailstar boat trailer for a boat with a seized engine that a friend is giving me. The trailer was a great deal, but they told me the lights worked and they didn't. The connections were all corroded, none of the side lights were hooked up, and there wasn't enough slack in the existing harness to connect anything to it. Your harness was plenty long and only $15! I just wish that the ground wire was as long as the other wires. The ground wire only reached to the front part of the trailer and there's a hinge with rubber bushings halfway along the tongue. I had to ground the front part of the tongue to the part after the hinge. And then I used the ground wire in the old harness to ground the taillights.

Show More Reviews

See what our Experts say about this Optronics Trailer Wiring

  • Troubleshooting Trailer Brakes that Lock Up When Connected to Junction Box
    Sounds like you are wiring the brake output circuit from your brake assemblies to a pin on the junction box that carries the 12 volt circuit and not the brake output circuit. You need to make sure that you have the right circuit for the brakes on the junction box.
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  • Can Electric Trailer Brakes Ground Through Aluminum Trailer Frame
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  • Trailer Wiring has 3 Wires for Brakes But Magnets Only have 2 Wires
    Electric trailer brake magnets only have a power wire and a ground wire (doesn't matter which is which). The power wires will attach to whichever of the 3 wires carries the brake signal from the brake controller. One of the other wires must be a ground but you can ground the magnets to any clean metal surface. The third wire could be for something else or it could be a power or ground that tees off from the main ground/power wire.
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  • Availability of Complete Replacement Trailer Wiring Harness for 1989 Wells Cargo Enclosed Trailer
    We do not offer complete OEM-style trailer wiring harnesses for specific trailers but we do carry all of the various connectors, plugs, sockets and other components required to re-wire a trailer from stem to stern. I have provided two links to our main pages for trailer connectors as well as two comprehensive articles on trailer wiring and troubleshooting.
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  • Trailer Left Turn and Brake Lights Sometimes Do Not Work on Trailer Towed by 2014 Kia Sorento
    This is a textbook example of a bad ground connection. Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light. Make sure that the vehicle side and trailer side connectors are clean and free of corrosion inside and out. The main connector grounds should be attached to clean and corrosion free bare metal surfaces. The light grounds should also be attached to clean and...
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  • Installing a Trailer Wiring Harness on a Trailer with Yellow, Black and White Tail Light Wires
    When it comes to tail light wiring, black is usually the running light circuit and white is usually ground. That would leave the yellow wire for the brake light and turn signal. On trailers, the turn signal and brake lights are combined on the same circuit. When installing a harness like the Optronics Wishbone 4-way Harness, # A35W42B, the green wire would connect to the yellow wire on the passenger side tail light and the brown wire with the green stripe would connect to the black wire...
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  • Half of the Lights on a 1973 Ideal Travel Trailer Are Not Working
    So is it half of the new lights that are not working? Regardless of if it is the new or old lights (assuming the old light were working before) there could be several issues causing half of the lights to not work. It could be a ground problem. Ground problems normally show up when there is more draw on a system such as when you have the running lights on and then use another function like a turn signal or brake light. Make sure that the vehicle side and trailer side connectors are clean...
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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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  • Troubleshooting Right Stop/Turn Circuit on Aluminum Trailer
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  • What Does Second Brown Wire of a 4-Way Trailer Connector with 5 Wires Connect To
    What you have a is a 4-way Wishbone trailer connector like part # A35W42B. The two brown wires are both the running light circuits. One needs to ran to each side of the trailer. This makes the wiring a little easier instead of having to run the brown wire to one side and then have a jumper wire to the other side.
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  • Wiring 3-Wire Lights to Boat Trailer with Wishbone 4-Way Harness
    It sounds like you are using a wishbone harness to re-wire your trailer. A wishbone connector has a brown/green wire for the running lights on the right side and a yellow/brown wire for the left side running lights. You will also have a yellow wire that is for the turn signal and brake lights on the left side, and a green wire that is for the right side turn signal and brake lights. The white wire, as you mentioned, is for ground. On your trailer lights, most likely the red wire is for...
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  • Replacing Wishbone Connector on Trailer with Traditional 4-Way Connector
    It sounds like the old connector on your trailer was a wishbone harness, which has two brown wires for the running light circuit (one for each side of the trailer) and the standard wires beyond that. To replace the connector with a traditional 4-Way like what you have now, you will just need to connect both of the brown wires on the existing wiring to the brown wire on the new connector. Yellow should still be for left turn/brake and green is for right turn/brake, both of which should...
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  • Recommended 4-Way Wiring Harness For Trailer Side
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  • Wiring in Amber Side Marker Trailer Lights that have Black and Yellow Wires
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  • Replacement 4-Way Recommendation for 2006 Blizzard Trailer
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