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Curt 56272 Custom Vehicle-Side Trailer Wiring Harness - 4-Flat Connector

CURT 56272 custom vehicle-side trailer wiring harness with 4-flat connector and factory plug-in connectors for no-splice installation
 
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List Price: $115.95
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Part Number: 56272
Manufacturer: Curt MFG

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CURT Manufacturing 4-Flat Connector No-Splice Install CURT 56272 Custom Vehicle-Side Trailer Wiring Harness

Get your trailer lights wired correctly the first time. The CURT 56272 is a vehicle-specific, plug-and-play wiring harness that connects directly to your factory tail light wiring -- no cutting, no splicing, no guesswork. It delivers clean, reliable trailer lighting signals through a standard 4-flat connector, keeping your tow vehicle's electrical system intact and warranty-friendly.

Plug-In Fit, Factory-Clean Results

CURT's custom wiring harnesses are engineered to match the specific tail light wiring architecture of select vehicle makes and models. The 56272 uses OEM-style connectors that plug directly into your existing tail light harness -- on one side to the vehicle, on the other side to the trailer's 4-flat plug. No T-one adapters, no stripped wires, no electrical tape bundles under the bumper.

This harness is part of CURT's broad custom wiring lineup, which covers hundreds of vehicle applications from late-model trucks and SUVs to minivans and crossovers. Each harness is designed to handle the vehicle's specific signal type -- whether that's a simple incandescent system or a more complex CANBUS-based lighting circuit -- and routes a clean, correctly converted signal to your trailer connector.

No-Splice Design

OEM-style connectors plug directly into factory tail light sockets -- no wire cutting or splicing required for a clean, reversible install.

4-Flat Trailer Connector

Standard 4-flat output (left turn/brake, right turn/brake, tail/running, ground) fits the majority of trailers, boat trailers, utility trailers, and RV tow dollies.

Vehicle-Specific Engineering

Matched to the exact wiring layout of compatible vehicles -- no adapter guessing, no resistor add-ons for most fitments.

Durable, Road-Ready Construction

Weather-resistant connectors and insulated wiring stand up to road spray, UV exposure, and the vibration demands of regular towing use.

What the 4-Flat Connector Does

The 4-flat (also called 4-pin flat) is the most common trailer connector standard in North America. It carries four functions on four flat pins arranged in a row:

  • Pin 1 (White): Ground
  • Pin 2 (Brown): Tail/running lights
  • Pin 3 (Yellow): Left turn and brake signal
  • Pin 4 (Green): Right turn and brake signal

This four-function layout supports all basic trailer lighting requirements -- tail lights, brake lights, and turn signals -- and is compatible with boat trailers, single-axle utility trailers, cargo trailers, and most lightweight RV accessories like tow dollies and small popup campers. It does not carry a dedicated brake controller circuit or 12V auxiliary power; for those functions a 5-flat or 7-way connector is required.

Plug-and-Play Advantage: Because the 56272 uses factory-matching connectors, installation typically takes 15-30 minutes with no special tools. Simply unplug the vehicle's tail light connector, insert the harness in-line, and route the 4-flat lead to your hitch area.

Typical Towing Applications

  • Boat trailers and personal watercraft trailers
  • Single- and tandem-axle utility trailers
  • Cargo and enclosed trailers with basic lighting only
  • Tow dollies used with motorhomes for flat towing a dinghy vehicle
  • Small popup campers and tent trailers wired for 4-flat
  • Landscape, lawn, and equipment trailers
CANBUS Compatibility Note: Many newer vehicles use CANBUS-managed lighting circuits that can trigger fault codes or burnt-out warning lights when a conventional T-connector draws extra current. CURT's custom harnesses for CANBUS vehicles include the appropriate circuitry to prevent these issues. Verify that the 56272 is listed for your specific vehicle year, make, and model before purchase.

Installation Overview

No wiring experience is required for a typical install. The general process is:

  • Open or remove the tail light access panel on your vehicle (usually in the cargo area or under the bumper trim)
  • Unplug the factory tail light connector on one or both sides
  • Plug the harness connectors in-line between the vehicle socket and the tail light assembly
  • Route the 4-flat lead along the frame to the hitch receiver area
  • Secure with included hardware or cable ties; test all functions before connecting a trailer
Maintenance Tip: Apply dielectric grease to the 4-flat connector pins annually, especially if you tow in wet or coastal environments. This prevents corrosion that causes intermittent lighting faults, which are a common roadside issue and a DOT inspection failure point.
May Also Need: If your trailer uses a 5-flat or 7-way connector, you can add a CURT 4-to-5 or 4-to-7 adapter at the trailer end -- no need to change the vehicle-side harness. CURT adapter part numbers 57000-series cover most configurations.

Product Specifications

ManufacturerCURT Manufacturing
Part Number56272
UPC612314562725
Harness TypeCustom vehicle-side, plug-and-play
Trailer Connector Type4-flat (4-pin flat)
Installation MethodNo-splice, in-line factory connector

Physical Dimensions

Package Length9.0 in
Package Width6.0 in
Package Height3.0 in
Shipping Weight1.68 lbs

Connector Functions (4-Flat Standard)

White Wire / PinGround
Brown Wire / PinTail / running lights
Yellow Wire / PinLeft turn signal and brake
Green Wire / PinRight turn signal and brake

Compatibility and Fitment

Fitment TypeVehicle-specific -- verify year/make/model via CURT fitment guide
Connector InterfaceOEM-matching factory tail light plug(s)
Trailer Types SupportedBoat, utility, cargo, tow dolly, popup camper (4-flat equipped)
CANBUS SupportIncluded where required for compatible vehicle applications

What's Included

Wiring Harness1x vehicle-side custom harness assembly
4-Flat ConnectorIncluded on harness lead
Mounting HardwareTypically included (zip ties or bracket; varies by kit)

What Is NOT Included

Brake ControllerNot included -- 4-flat does not support electric brakes
12V Auxiliary PowerNot provided -- upgrade to 7-way for battery charging
Trailer-Side WiringNot included -- this is the vehicle-side harness only
Hitch ReceiverNot included -- sold separately
Important Information -- Read Before Installing
  • Verify vehicle fitment using CURT's online fit guide with your exact year, make, model, and trim level before installing. Using the wrong harness can cause lighting faults or ECU warnings.
  • The 4-flat connector supports tail lights, turn signals, and brake lights only. It does NOT carry electric brake signals or 12V auxiliary power. Do not connect a trailer with electric brakes to a 4-flat connector.
  • Do not exceed the rated current capacity of the harness circuits. Overloading by connecting LED light bars or non-standard trailer accessories through this harness can damage vehicle lighting circuits.
  • On CANBUS-equipped vehicles, using a generic T-connector instead of the correct custom harness may trigger dashboard warning lights or blow fuses. Use only the vehicle-matched CURT harness.
  • Inspect the 4-flat connector and all wiring for chafing, corrosion, or loose seating before each towing season. A failed ground is the number-one cause of erratic trailer lighting behavior.
  • This harness is for the vehicle (tow vehicle) side only. Trailer-side wiring is not included and must be purchased separately if needed.


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