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40 Ft 5-Way Trailer Wiring Harness - Wishbone Style - 30" Ground - 5' Auxiliary Wire

40 Ft 5-Way Trailer Wiring Harness - Wishbone Style - 30" Ground - 5' Auxiliary Wire

Item # A40W5B
Our Price: $40.03
Trailer Wiring
Shipping Weight: 1.38 lbs
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40 Ft 5-Way Trailer Wiring Harness - Wishbone Style - 30" Ground - 5' Auxiliary Wire 5 Flat A40W5B
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5-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. Auxiliary wire signals trailer brakes to disengage when in reverse. Great Prices for the best trailer wiring from Optronics. 40 Ft 5-Way Trailer Wiring Harness - Wishbone Style - 30" Ground - 5' Auxiliary Wire part number A40W5B can be ordered online at or call 1-800-940-8924 for expert service.
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Optronics Trailer Wiring - A40W5B

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

5-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. Auxiliary wire signals trailer brakes to disengage when in reverse.


  • 5-Way trailer harness connects to your tow vehicle to control trailer light functions
    • Ideal for marine trailers with hydraulic or surge brakes
  • 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
  • Auxiliary wire (blue) connects to backup light circuit to disengage surge brakes when you are driving in reverse
    • Hydraulic actuator must have electric lockout feature built-in to disengage the trailer brakes
  • Color coded wires help with installation
    • White - ground
    • Brown - tail lights
    • Yellow - driver side stop/turn
    • Green - passenger side stop/turn
    • Blue - auxiliary wire


  • Wire harness length: 40'
  • Ground wire length: 30"
  • Auxiliary wire length: 5'

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

  • Truck Lite # 002295

A40W5B Optronics 40 ft. Wishbone 5-Way Trailer Harness with 30" Ground and 5 ft. Blue Wire

Alternate part number: A-40W5B

California residents: click here

Customer Satisfaction Score:

Customer Reviews

40 Ft 5-Way Trailer Wiring Harness - Wishbone Style - 30" Ground - 5' Auxiliary Wire - A40W5B

Average Customer Rating:  4.8 out of 5 stars   (143 Customer Reviews)

5-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. Auxiliary wire signals trailer brakes to disengage when in reverse.


My boat trailer had a split wiring harness that had suffered over the years. I purchased this harness for the boat trailer and with attaching it to the old wire was able to pull it through the frame and connect all new lights in an afternoon.


Fast n easy!! Exactly what I needed.


Great Quality. This harness has 20ga wire. wish the wire gauge was thicker. I used this for a boat trailer rewire and 16ga would beef the harness up perfectly.


This harness worked well for my 21 foot boat trailer. There was excess wire and it took care of some corrosion problems I had with my old wiring.
Etrailer always has great descriptions so you know what is being shipped.


Easy installation


Product is quality and order came oerfe ctly


Just what I was looking for. I believe this is going to work as I run the wire from the front of my 5th Wheel to the back.

John B.


It is working out fine. Thanks Etrailer.


The harness seems fine but receiving this item from etrailer was terrible. I didn’t have enough in my cart for free shipping so I was charged, which is fine. What I am not fine with is etrailer using the pony express to get it to me. If I can find it on [online vendor] I will get it from there.


I guess I should of read discription better , wire harness delivered had 4 wires that were 30’ in length , but the blue and white wires were only 36” in length , I had to go out and but a roll of white and a roll of blue to complete replacement PU camper break circuits.

Etrailer Expert

Jenny N.


This harness comes with 40 foot of the brown, yellow, and green whites. It comes with 30 foot of the white ground wire and 5 foot of the blue auxiliary wire. The auxiliary wire connects to backup light circuit to disengage surge brakes when you are driving in reverse. The hydraulic actuator must have electric lockout feature built-in to disengage the trailer brakes


Etrailer is awesome
Great website for
detailed parts
I buy from etrailer all the time

Jim M.


Great etrailer is awesome


Wry impressed with how quick the items came. I ordered some other items the day later and still waiting for them but overall very happy.




I got my 40ft wishbone trailer harness in about 5 days. Was held up a day because of the Christmas holiday. All in all I was quite satisfied with my purchase. I'm putting "Pole Lights" on my trailer to keep them out of the water. I didn't want to "splice any wires", so I ordered the 40ft length. I have not yet installed this, but plan to start today. Its been a very busy holiday season, and now time to get to work.

Capt. Jim Hedgecock


Last Fall I ran new trailer wiring for my boat trailer. This wiring was great for the application and trailer lights work great today.


Design wise it is excellent, the wishbone design is intelligent and makes rewiring a boat trailer simple and clean.

The Good rating? The wire gauge looks to be 18-20, wish it was heavier gauge, especially since it is a 40 ft long harness. And it is made in China or Taiwan, not a heavy duty or perfect construction.

If it lasts as long as my original, 14-years, I'll come back and bump up my rating, and I bet you can't find a better one.

As far as the transaction, it was excellent, had the 40 footer I needed, great price and super fast shipping.


Great product


etrailer is a the only place I could find this item as I live in a rural area. The harness was perfect and did the job well. Service and shipping time was perfect.


Very satisfied with product. Only recommendation is charge an extra minimal amount for splices, terminals and etc.
In my DIY application, replacing the bumper plug connector. I'll retain the remaining wiring harness for near future replacement.


Rep knew what I needed and did a great job of selecting and sending the item to me. I recommend these folks very highly


nice wire and plug setup. Its better to change the whole wiring harness if the wire is getting stiff.


Product was shipped quickly and matched the product description. Tried to find it locally for a price comparison but nobody stocked this item. Shopped online and had the best price. Good product, good service. Thank you.


My 5 pin, 40' wire harness arrived within just a couple days. Excellent price and Excellent service. Thank you


Completely rewired my trailer and this kit had all that I needed.


Great company to deal with. Very prompt getting my product to me. Also, the kept me continuously updated on when I would receive it. I would highly recommend etrailer.


Very pleased with my 40’ 5 pin trailer harness. Highly recommend these guys!

Show More Reviews

See what our Experts say about this Optronics Trailer Wiring

  • Wire Gauge Size of the 40 Ft 5-Way Trailer Wiring Harness A40W5B
    The 40 Ft 5-Way Trailer Wiring Harness part # A40W5B uses 20 gauge wire according to Optronics. This is pretty standard and will work for the vast majority of trailers without issue.
    view full answer...
  • What Wire Does The Yellow Wire With Brown Stripe On My Trailer Connect To
    On the trailer's 5-way connector the yellow wire with brown stripe is most likely a running light circuit but you want to be sure. There is sometimes a yellow/brown wire which is ran down the left side of the trailer for tail lights and a green/brown wire which is ran down the right side of the trailer for tail lights. Since wire color functions may vary depending on the manufacturer you still want to test the wire to determine the function by using a vehicle battery and jumper wire on...
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  • Why Does Wishbone Trailer Wiring Harness A40W5B Have Extra Brown Wire
    I could not find etrailer order history for you based on either your last name or your email address so I do not know which vehicle wiring harness you have. The linked page shows the 4-pole trailer wiring kits we offer for your 2008 Nissan Sentra. This is the only type of wiring kit we have for this vehicle. Some trailer wiring kits will use dual running light wires to avoid the need to splice and run that circuit's wire across the sides of the trailer. These are called wishbone harnesses...
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  • Where Does Blue Wire of Trailer Wiring 5-Way Normally Run to on Trailer
    So the blue wire of the 5-ways like the # A40W5B normally runs to the reverse lockout solenoid of a surge brake actuator like what you described having. The blue wire on the vehicle side of the wiring runs to the reverse light circuit. This allows the solenoid to have voltage when the vehicle is put in reverse preventing the brakes from applying. This runs right to the back of the actuator on the trailer coupler which is why you don't see the wiring ran to the back of the trailer.
    view full answer...
  • 5-Way Wiring Harness for Boat Trailer
    A wishbone harness means that there are separate wires for the running light circuits - one for each side of the trailer. For a 5-flat trailer end connector for your Ranger boat trailer, a great choice would be the 5-Flat Connector # A40W5B.
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  • Determining Wiring Functions On Trailer To Install New 4-way Connector
    Typically there is a white, green, brown, Yellow/Green and brown, and a yellow wire so since you do not have a dedicated yellow wire you will need to test wire functions by using connecting the brown, green, yellow/brown, and green brown one at a time to the positive terminal of a battery while grounding the white wire and seeing which functions come on with each wire. Since the colors on your old connector are not standard you will need to make the connections by function and not the color...
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  • 5-Way Recommendation For Trailer that Was Converted to Disc Surge Brakes
    What you would want is the part # A40W5B which is a trailer side 5-way flat with 40 inches of wiring. 5-Way rounds aren't common for trailer towing so that wouldn't be your best option. What you'd then want to do is cut all of the wires but the blue to length so that you can wire the 4 wires of the 5-way to your current wiring near the coupler, and then leave the blue wire longer so that it can make it to your reverse lockout solenoid.
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  • Does The Wesbar 5-Pole Flat Connector W002290 Use Copper Wire Or Copper Clad Wire
    The Wesbar 5-Pole Flat Connector W002290 (along with virtually every other wiring harness we sell) uses full copper wire. Unfortunately the Wesbar W002290 is no longer available. We now offer the Optronics # A40W5B which is a similar 5-flat harness that also uses full copper wire.
    view full answer...
  • Trailer Wiring Harness With Tinned Wire
    While tinned wiring is the norm when it comes to interior wiring on boats, boat trailers see a minimal amount of water compared to the actual boats. They do use a tin coating on the pins that are the parts of a wiring harness like the Wesbar 5-Pole Flat Connector # A40W5B since those are most exposed to moisture, but since the actual wiring is rarely exposed to water I'm guessing that's why they don't go the extra mile when it comes to using that wiring within the harnesses. As far as...
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  • Is Tinned Wiring Used In Trailer Wiring Kits
    The trailer wiring we offer like part # A40W5B, is designed to be used as a 5-wire harness, and works well with a trailer that has a surge coupler. The wires used in this harness are 16 gauge except the blue brake wire which is 18 gauge, and designed to be able to safely handle the current from a 12 volt system. The wires in this harness are not tinned. From my research I found that tinned wire is normally used in industrial wiring and used when the operating temperature of the wire is...
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  • Trailer Wiring Connector for Triton 8x10 Aluminum Snowmobile Trailer
    For your wiring, you will need to test your wire functions to know which one connects where. I recommend using a 12v battery and simply connecting the negative terminal to the trailer frame and then connecting the power to each wire at the connector individually to determine function. It is not uncommon to have two wires running to one function location for each side of the trailer so there aren't any jumper wires across the frame needed from side to side. I've attached an article...
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    Image 1 for Image 2 for
  • Wishbone Trailer Wiring Harness for a Magic Tilt Boat Trailer
    I believe you have what is referred to as a wishbone wiring harness. A wishbone wiring harness has 6 wires and is the same as a 4-way for the exception that it has both running light wires ran to the trailer connectors as opposed to splicing them together and then running them to the trailer connector. The functions should be as follows: Green - Right Turn/Brake Yellow - Left Turn/Brake Yellow/Brown - Left Running Light Green/Brown - Right Running Light White - Ground Red - Reverse Lockout...
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  • Recommendation to Replace Trailer 5-Way That Has 9 Wires
    It sounds like the current 5-Way connector on your trailer has a type of wishbone wiring design, which uses separate wires for the signal lights on both sides of the trailer. Most likely yours has a separate wire going down each side of the trailer for the running lights, brake lights, and reverse light functions. I highly recommend following the wiring from the connector on your trailer and testing them for function to verify this. We do not have any 5-Way connectors available with a...
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    Image 1 for
  • Available 5-Flat Wishbone-Type Trailer Connectors
    We do not carry (and I have not seen) a 5-flat type trailer connector with the many multiple wires for each pin that you describe. We DO have wishbone 5-flat connectors like # A40W5B which have two brown running light wires to simplify connection to the tail lights on both sides of a trailer. What you describe sounds like a custom-made part. I can understand the three white (ground) wires especially if the trailer were made of aluminum which makes establishing multiple grounds more challenging...
    view full answer...
  • Wiring Needed to Connect Surge Brake Reverse Lockout to Trailer Wiring
    Not every boat trailer will have the reverse light circuit completed so you'll just need to complete this circuit. Most likely you have a 4-way now so you'd want to swap that out to a 5-way and run the 5th circuit to the reverse lock out solenoid. For that we have the part # A40W5B. The other wire of the solenoid will need to ground to the trailer frame.
    view full answer...
  • Replacing 5-Way Trailer Harness That Has 7 Wires
    When a 4-Way or 5-Way pin wiring harness for a trailer has more wires than pins, like the Optronics # A40W5B, it just means that the manufacturer is trying to make it easier on the installer. In your case it sounds like your trailer has 2 ground wires and 2 running light wires that run down either side of the trailer. If this is the case then all you have to do is splice the browns together and the whites together with your new harness and everything should work great! I have attached...
    view full answer...
  • Old Trailer Wiring 5-Way had 6 Wires But New 5-Way Has 5 Wires
    The trailer connector that you had is what is called a wishbone harness. It has 2 running light wires so you do not have to run a jumper wire for running lights from one side of the trailer to the other. Harness # A40W5B is an example of a wishbone 5-Way. All you have to do is connect the 2 running light wires from the trailer wiring together and then to the brown wire on the new harness. Or, if you are replacing all the wiring, you would run a jumper wire from one side of the trailer...
    view full answer...
  • Recommended 5-Way Flat Harness With 16 Gauge Wire Over 25 Feet Long
    For that length, I recommend the 5-Pole Flat Connector # A40W5B. This has 16 gauge wires with the exception of the blue wire that is 18 gauge.
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  • Replacing 5-Way on Trailer that Used 8 Wires
    The # A40W5B would be a really great choice although it only has 5 wires ran to it. You'd just need to combine all of the similar wire colors to the single circuit of the new 5-way. The brown and brown/green would go to just the brown of the new 5-way.
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  • 4-Way Trailer Wiring Recommendation for a Utility Trailer
    A 5-way is usually seen on trailers that have either reverse lights or a reverse lockout for a surge brake system. If you have no need for a 5-way you could use a 4-way like the part # W787268. If you did want to install a 5-way you would want the part # A40W5B. A 4-way connector on a tow vehicle would still plug into a 5-way on a trailer. The fifth circuit just wouldn't be active. To make the install simpler and cleaner a junction box like part # 38656 would be a great option. Check...
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  • What are the Functions of a 4-Way Flat Trailer Wiring Connector with 5 Wires
    What you are describing is called a wishbone harness. This is different than a 5-Way flat connector like # A40W5B that you have referenced. A wishbone harness will have 5 wires, 2 of them going to the running light pin which is right next to the ground pin. This is so you do not have to splice in a jumper wire to go from one tail light to the other for the running light function. A 5-Way flat will have 5 wires (though there are also wishbone 5-Ways) and the extra pin is usually attached...
    view full answer...
  • How to Replace a 5 Pole Flat Wiring Harness That Has 7 Wires
    I have a solution for you, but we do not have the exact replacement for this wiring harness. Instead, I recommend using the 5-Pole Flat Connector # A40W5B to replace your old connector and then combine one of the wiring functions on the old harness into one wire on the new harness. You'll want to test the functions of your existing wires but my best guess is that the way this is currently wired your blinkers have individual ground wires and that harness has no reverse light wired in- these...
    view full answer...
    Image 1 for
  • Replacement Trailer Wiring Harness For a Boat Trailer Using a 5-Way Flat Connector
    Currently the only wiring harnesses we have with a 5-way flat connector are like the 25 Ft 5-Way Trailer Wiring Harness # A25W5B and 40 FT Harness # A40W5B. These harnesses use 6 wires coming from the connector. It has a short 5' blue wire to run to the surge brake electric lockout, a short 30" ground wire to attach to the trailer frame, 2 brown wires for the running lights on either side of the trailer, a green wire for the passenger brake/turn signal and a yellow wire for the drivers...
    view full answer...
  • Replacement Trailer Side Wiring Harness for a 1996 Yacht Club PWC Trailer
    Trailer side wiring harnesses are not specific to the trailer so you can use any one that has the proper connector and length for your 1996 Yacht Club PWC trailer. I have included a link to the trailer side harnesses for you. If your trailer has a 4-Way flat connector a popular option is wishbone harness # A35W42B. A wishbone harness has 2 wires connected to the running light pin so you won't have to run jumper wires from one side of the trailer to the other for running lights. If your...
    view full answer...

Do you have a question about this Trailer Wiring?

Info for this part was:

Employee Michael H
Expert Research:
Michael H
Employee Jameson C
Expert Research:
Jameson C
Employee Brian T
Updated by:
Brian T

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