Trailer Wiring Harness Guide (Canada)

Trailer wiring

A hitch holds the trailer. Wiring makes the lights and often the brakes work. Match the plug on your trailer, choose a vehicle-specific harness when one exists, and use adapters only when the circuits you need are already present on both sides.

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Adapter · four-flat to seven-wayCURT 57184$40.27 CADSee the part →

Four-way versus seven-way in plain English

A four-way flat plug carries running lights, brake lights, and turn signals. That is enough for many light utility trailers. A seven-way blade plug adds electric-brake output, a twelve-volt charge line, and usually reverse lights. If the trailer has electric brakes, plan on seven-way at the vehicle and a brake controller inside.

Adapters can map lights between plug styles. They do not add a brake circuit that is not there. If you only have four-way on the vehicle and the trailer wants electric brakes, you need a proper seven-way install and a controller, not just an adapter.

Vehicle harness versus converter

Many late-model trucks and SUVs take a CURT T-connector harness that plugs at the taillight connectors and presents a four-way or seven-way at the bumper. That is the cleanest answer when the product page names your year. Older vehicles without a dedicated tow circuit may need a taillight converter that reads the vehicle lamps and drives the trailer lights without confusing the body computer.

Always read the product application. Some harnesses exclude factory tow packages. Others need a module seat. Canadian road salt eats trailer plugs. Dielectric grease and a plug cover help after winter trips.

Wiring parts we commonly sell

CURT part 57184Adapter · four-flat to seven-wayMaps four-flat vehicle lights into a seven-way trailer plug for light-only jobs.$40.27 CAD

CURT part 57185Adapter · four-flat to seven-way with bracketSame light-mapping job with a bracket so the adapter has a home.$49.67 CAD

CURT part 57240Adapter · seven-way to four-flatWhen the vehicle already has a seven-way and the trailer is four-flat.$18.10 CAD

CURT part 57102Adapter · seven-way and four-wayThe common seven-way to four-way adapter. Confirm genders on the product page.$75.07 CAD

CURT part 56236Taillight converterThe converter for when a T-connector harness is not the right answer.$103.98 CAD

CURT part 56187Powered taillight converterPowered three-to-two converter for listed vehicle lighting setups.$54.47 CAD

Official CURT wiring context

Official clips from @curtmfg. Cap is two embeds. Use the product-page video for your exact harness when one exists.

Related guides

Four-way versus seven-wayWhich plug you actually need

Adapter mistakesWhat adapters cannot do

Brake controllerWhen seven-way is not enough alone

Plug corrosionSalt and brine habits

Hitch buying guideReceiver first

Towing guides hubAll guides