CURT 56040 Vehicle-Side 4-Pin Trailer Wiring Harness - Easy Plug-In

In this review of the CURT 56040 trailer wiring harness the bottom line is simple: this is a smart, no-fuss solution for Subaru owners who need a standard 4-pin trailer connection without cutting or splicing vehicle wiring. Designed specifically for select Subaru Ascent, Forester, Outback, Crosstrek and XV models, the harness plugs into the factory wiring and provides reliable power to trailer tail lights, brake signal lights and turn signals. It is best for DIY owners who want a clean OEM-style install and dependable lighting performance for routine towing.

Key Features

• Easy to install: The plug-in T-connector design requires no cutting, splicing or soldering, so installation is fast and reversible.
• Standard 4-pin connector: Supplies tail, brake and turn signal circuits with a universal 4-flat plug for common trailers.
• Vehicle-specific fit: Custom-fitted for select Subaru Ascent, Forester, Outback, Crosstrek and XV models to ensure correct connector placement and minimal routing.
• Reliable power delivery: Built with surface mount technology to produce less heat and maintain consistent light intensity under load.
• Weather protection: Includes a rubber dust cover to protect the 4-way flat connector from moisture and dirt when not in use.

Who It's For

This harness is ideal for Subaru owners who tow occasionally and want a simple, OEM-compatible wiring solution that preserves factory wiring integrity. DIYers who prefer a plug-and-play approach will appreciate the minimal tools and time required for installation.

Its less appropriate for users who need a 7-way connector, integrated trailer brake control, or custom wiring beyond basic lighting circuits. If a vehicle does not appear on the compatibility list, owners should seek a model-specific harness for their make and year.

Pros & Cons

Pros

• Plug-in installation saves time and avoids permanent changes to the vehicle wiring.
• Custom fit for specified Subaru models results in clean routing and secure connectors.
• Durable construction and surface mount circuitry deliver consistent light performance.
• Includes a rubber dust cover to extend connector life in outdoor conditions.

Cons

• Only provides a 4-way flat connector, so owners needing auxiliary power or brake controller wiring must purchase additional adapters.

Specifications

Brand	CURT
Connector type	4-pin 4-flat trailer connector
Vehicle fit	Select Subaru Ascent, Forester, Outback, Crosstrek, XV
Installation	Plug-in T-connector, no cutting or splicing
Protection	Rubber dust cover for weather resistance
Circuit technology	Surface mount technology for reliable power

Our Verdict

The CURT 56040 is a practical, cost-effective option for Subaru drivers who need a dependable 4-way trailer lighting connection without modifying factory wiring. Its vehicle-specific fit, easy plug-in installation and durable components make it a good value for routine towing tasks, provided a 4-pin connector meets your needs.

Frequently Asked Questions

Will this harness require cutting into my vehicle wiring?
No. The harness uses a vehicle-side OEM-compatible plug so no cutting or splicing is required.

Does the harness support brake controller functions?
The 4-pin connector supplies tail, brake signal and turn lights but does not provide a dedicated brake controller circuit or 12V auxiliary power.

Is the connector weather resistant?
Yes, the kit includes a rubber dust cover to protect the 4-flat connector when not in use.