Towing Basics: Hitches, Brake Controllers and Wiring

Towing is a chain of parts that all have to agree: the hitch on the frame, the ball mount and ball, the wiring, the brake controller and the safety chains. Each link has its own rating, and the lowest one counts.

Start with your vehicle's ratings

Read the owner's manual and the driver's door-jamb label for:

• Maximum trailer weight (towing capacity). It often changes with engine, axle ratio, cab, box length and 2WD or 4WD, so read the line for your exact truck.
• Maximum tongue weight: the downward load the trailer may put on the hitch.
• Payload and GVWR: tongue weight counts against payload, along with passengers and cargo.
• GCWR: truck, load and loaded trailer together.

Trailer weight means the trailer as loaded, not its empty weight. Near a limit, weigh the rig at a public scale.

Receiver hitches: classes and sizes

Hitch class tells you roughly what receiver opening to expect:

• Class 1 and 2: 1-1/4 in (about 32 mm), for cars, small SUVs, bike racks and light trailers.
• Class 3 and 4: 2 in (about 51 mm), common on half-ton and mid-size trucks and SUVs.
• Class 5: heavy duty, usually 2 in or 2-1/2 in (about 64 mm), and 3 in on some heavy-duty pickups.

Ratings within a class vary by maker, so use whichever is lower: the hitch label or the vehicle rating. Hitches bolt to vehicle-specific frame points: in Trailer Hitches, each product page lists the years, makes and models it fits, or use the vehicle selector. In salt country, pull the ball mount between trips and grease the hitch pin; a mount left in all winter can rust in place.

Ball mounts: rise, drop and ball size

The ball mount sets the height of the ball, and the goal is a trailer that rides level. A nose-high or nose-low trailer loads its axles unevenly and is more prone to sway. To size it:

• With the truck loaded as it will tow, on level ground, measure from the ground to the upper edge of the receiver opening.
• Level the trailer and measure from the ground to the underside of the coupler.
• If the receiver is higher, the difference is the drop you need; if the coupler is higher, it is rise.

Lifted and levelled trucks often need a long drop. Three sizes must also match: the mount's shank to the receiver, the ball's threaded shank to the hole in the mount, and the ball to the coupler. Common ball sizes are 1-7/8 in, 2 in and 2-5/16 in, and the coupler is stamped with the size it takes.

If you tow more than one trailer, an adjustable mount saves swapping parts: the B&W Tow & Stow Ball Mount with 2-5/16" & 2" Balls lists a 5-inch drop, a 5-1/2 inch rise and both ball sizes in its title; check the product page for how it adjusts. Mounts carry ratings too; the Weigh Safe 6" Drop Hitch, 2" Shank states a 10K/15K gross tongue weight rating in its name. More in Ball Mounts & Hitch Balls.

Tongue weight vs trailer weight

Trailer weight is the whole loaded trailer; tongue weight is the part pressing down on the ball. For a conventional bumper-pull trailer, a common rule of thumb is roughly 10 to 15 percent of loaded trailer weight. Too little and the trailer tends to sway; too much and it lifts weight off the truck's front axle, lightening steering and braking. Load heavy cargo slightly ahead of the trailer axle and check with a tongue weight scale. If the truck squats noticeably once hitched, a weight-distribution hitch spreads the load; your owner's manual says when one is needed.

Brake controllers: proportional vs time-delay

A trailer with electric brakes needs a brake controller in the truck to apply them. Hydraulic surge brakes, common on boat trailers, work on their own.

• Proportional: a motion sensor reads how hard the truck is slowing and brakes the trailer to match. Stops are smoother and the trailer pushes less. Mount it within the angle the maker specifies and level or calibrate it.
• Time-delay: pressing the pedal ramps the trailer brakes up to a preset level over a set time. Simpler, but light stops can feel grabby and hard stops late.

Set the gain with the trailer loaded: at low speed on dry, level pavement the trailer brakes should bite firmly without locking. Turn it down on snow and ice. Most controllers mount under the dash on a vehicle-specific plug-in harness; many newer trucks have one built in. In Brake Controllers, check each product page for the controller type and the harness it needs.

Wiring: 4-pin vs 7-pin

• 4-pin flat: running lights, left turn and brake, right turn and brake, ground. Enough for a light utility trailer without electric brakes.
• 7-pin round blade (RV style): the same plus an electric brake circuit, a 12-volt auxiliary line that can charge a trailer battery, and reverse lights. Required for electric brakes.

Salt and slush corrode pins fast: keep the cover closed, use dielectric grease on the contacts, and test every light before each trip. A poor ground causes most dim or flickering trailer lights. See Towing Wiring & Lighting.

Safety chains and breakaway

• Cross the chains in an X under the tongue so they cradle it if the coupler comes off the ball.
• Leave slack for tight turns, but not enough to drag.
• Hook to the chain loops on the hitch, never the bumper or ball mount.
• Use chains and hooks rated for at least the loaded trailer weight.
• Attach a breakaway cable to the truck on its own, not to a chain, so it can apply the trailer brakes if the trailer separates.

Rules on trailer brakes, breakaway systems, chains and mirrors vary by province. Check your province's rules before you tow.

FAQ

Can I use a 2 in ball on any trailer?

No. The ball must match the size stamped on the trailer coupler. A coupler made for a 2-5/16 in ball will not latch safely on a 2 in ball and can lift off on a bump.

Do I need a brake controller?

If the trailer has electric brakes, yes: without a controller they do nothing. Whether a trailer must have brakes depends on its weight and where you drive, and the thresholds differ between provinces, so check your province's rules and your owner's manual.

Can I tow a trailer with electric brakes on 4-pin wiring?

No. A 4-pin flat connector has no brake circuit. You need a 7-pin connector wired to a brake controller.