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Curt 56325 Custom Fit Trailer Wiring Connector -- 4-Pin Flat T-One Harness

CURT 56325 custom fit T-one 4-pin flat trailer wiring connector harness for vehicle-specific plug-and-play towing light integration
 
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: $19.65
Part Number: 56325
Manufacturer: Curt MFG

Quantity in Stock :226

Availability: In Stock
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CURT Mfg4-Pin FlatNo-Splice InstallCURT 56325 Custom Fit Trailer Wiring Connector -- Plug-and-Play 4-Pin Flat Harness

Stop fighting with wire taps and electrical tape. The CURT 56325 is a vehicle-specific T-one wiring connector that integrates directly into your tow vehicle's existing tail light harness, delivering clean trailer lighting output through a standard 4-pin flat connector -- no cutting, no splicing, no voided warranties.

Clean Tow Lighting Wiring Without the Mess

The CURT 56325 belongs to CURT's T-One Connector product family -- custom-engineered harnesses designed to match specific vehicle makes, models, and years exactly. Rather than using generic T-taps that pierce insulation and invite corrosion, the 56325 uses a vehicle-matched plug-in design that routes between your factory tail light plug and the tail light itself. The result is a factory-quality connection that powers your trailer's running lights, brake lights, and turn signals without disturbing OEM wiring.

The outboard end terminates in a standard 4-pin flat connector -- the most common trailer wiring standard in North America -- compatible with virtually every utility trailer, boat trailer, cargo trailer, camper, and small travel trailer on the road. If your trailer has a 4-flat plug, this harness is ready to connect.

No-Splice T-One Design

Plugs directly into factory tail light connectors. No wire cutting, no tape, no taps into insulation. Preserves OEM wiring integrity.

4-Pin Flat Output

Standard North American 4-flat trailer connector carries running lights, left turn/brake, right turn/brake, and ground -- covers the vast majority of trailered loads.

Vehicle-Specific Fit

Engineered to match exact vehicle connector geometry and circuit configuration. No adapters needed. Harness length and plug positions are pre-measured for the target application.

Integrated Circuit Protection

CURT T-One harnesses include a circuit-protected module that isolates trailer lighting load from vehicle circuits, protecting sensitive factory electronics and LED driver modules.

Why Vehicle-Specific Wiring Matters

Modern tow vehicles -- especially those with LED tail lights, body control modules, and CANbus-monitored circuits -- are sensitive to electrical load changes. Generic T-tap wiring can trigger false bulb-out warnings, confuse BCM diagnostics, or overdraw LED driver circuits. The 56325's plug-in integration and built-in converter/isolator module prevents those issues by drawing power appropriately and keeping trailer circuit load off the vehicle's monitored signal lines.

Plug-and-Play Installation: Most installations take under 30 minutes with basic hand tools. No multimeter, no crimping, no stripping. Locate the tail light connector, unplug it, insert the T-one harness in-line, route the 4-flat to your hitch area, and done.

What Functions Are Wired

  • Left turn and brake signal
  • Right turn and brake signal
  • Tail/running lights
  • Ground (chassis common)

This is a standard 4-wire/4-pin flat configuration. It does not carry 12V auxiliary power, reverse lights, or electric brake output. If your trailer requires brakes or a 12V charge line, you will need a 5-pin or 7-pin connector solution in addition to or instead of this harness.

Trailer Compatibility: The 4-pin flat output on the 56325 is universally compatible with utility trailers, boat trailers, PWC trailers, landscape/lawn trailers, small cargo trailers, and most pop-up and teardrop campers. It is not intended for trailers requiring electric brakes or breakaway battery charging.

Installation Overview

  • Locate factory tail light connectors behind each lens or in the cargo/trunk area
  • Unplug the OEM connector and insert the T-one harness leads in-line
  • Route the 4-flat connector along the vehicle underside toward the hitch
  • Secure with included hardware or zip ties (not included on all kits)
  • Test with a trailer or 4-flat circuit tester before first tow
Maintenance Tip: Apply dielectric grease to the 4-pin flat connector before each season to prevent pin corrosion, especially if towing boat trailers exposed to water and salt. Replace the connector if pins show green oxidation or if any function becomes intermittent.

Connector Specifications

ManufacturerCURT Manufacturing
Part Number56325
UPC612314563258
Connector TypeT-One vehicle-specific plug-in harness
Output Connector4-pin flat (standard North American)
Install MethodNo-splice, plug-in integration
Circuit ProtectionIntegrated converter/isolator module

Physical Dimensions

Package Length9.0 inches
Package Width4.0 inches
Package Height2.0 inches
Shipping Weight0.29 lbs

Wiring Functions

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

Compatibility Notes

CURT Product FamilyT-One Custom Fit Connectors
Trailer Connector Standard4-pin flat (SAE J1239 compatible)
Trailer TypeNon-brake trailers: utility, boat, cargo, PWC, pop-up camper
Electric Brakes SupportedNo -- 4-pin flat only
Breakaway Charge SupportedNo -- requires 5-pin or 7-pin harness

In the Box

IncludedT-one wiring harness with integrated converter module and 4-pin flat pigtail
Not IncludedMounting hardware, zip ties, trailer connectors, wiring extensions
Important Information
  • This is a 4-pin flat connector -- it does NOT support electric trailer brakes. If your trailer has brakes, you need a 7-pin or 5-pin harness with a brake controller circuit.
  • Verify vehicle fitment before ordering. CURT T-One harnesses are year/make/model specific. Using the wrong harness can result in wiring that does not reach or connectors that do not mate properly.
  • Do not exceed the rated trailer lighting load for this harness. It is designed for trailer lighting only -- do not attempt to power accessories (refrigerators, inverters, chargers) through the 4-flat connector.
  • If your vehicle has LED tail lights or a CANbus/BCM-monitored system, use only vehicle-specific plug-in harnesses like this one -- generic T-taps can trigger fault codes and warning lights.
  • Inspect all connections before each tow. A loose or corroded 4-flat connection can result in non-functional trailer brake lights, a serious safety and legal hazard.


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