The most common connector types in use are the flat four-pin, the round six-pin, and the latest seven-pin style. There is also a five-pin type as well.
If there is a mismatch between the tow rig connector and the trailer connector, you can often mate the two with an adapter that is commonly available at auto suppliers. You'll always want the tow vehicle connector to have a greater number of electrical pins than the trailer connector in order to retain all the electrical features of the trailer.
This is an example of a hydraulic surge brake actuator. These are commonly used on boat trailers. This type of system uses no electrical braking information from the tow vehicle. The coupler senses an inertial pressure difference or "push" between the tow vehicle and the trailer when the tow vehicle starts to slow down. When this occurs, a rod inside this coupler box presses on a brake master cylinder to apply braking pressure to disc or drum brakes at the trailer wheels. Greater or lesser braking is applied automatically based on the slowing rate of the tow vehicle.
Here's the view of the rear of a surge brake actuator. You can see the brake master cylinder inside the housing. One often overlooked maintenance item is that of checking the fluid level in these actuators. Also, there is typically a braking disable device (electrically actuated or manually inserted pin) that can be applied if the trailer must be backed up a slope, a condition that would normally apply the brakes through the surge actuator.
This is an unmounted electric drum brake unit with backing plate. Its back flange mounts to a trailer flange and a drum is placed over the brake shoes. When voltage is applied to the magnetic actuator (arrow) it pushes outward on the shoe(s) to engage the braking function.
Another trailer safety device found on trailers with electric brakes is a breakaway activation system. This consists of a small cable that connects between the tow vehicle and the trailer. Should the two become disconnected, the cable pulls a pin on the breakaway switch (left arrow) and activates the electric brakes. A small battery mounted in a plastic box (right arrow) on the trailer tongue provides the needed power to apply the brakes on a runaway trailer and bring it to a halt.
In the case of a trailer that has electric brakes or a hydraulic surge brake unit, the breakaway cables and/or chains must be connected properly. If the connection length is incorrect, it may be possible for the brakes to become activated during sharp turning or other normal towing situation. If this happens, the brakes may apply without the driver's knowledge. If towing continues, the brake assembly can overheat and destroy axle components.
When using electric brakes, a small controller is installed in the cab of the tow vehicle and wired into the brake lighting. When the brakes are applied, voltage is transmitted to the trailer to engage the brakes. A manual sliding switch on the controller also allows you to apply only the trailer brakes with tow vehicle brake activation. There are two main types of brake controllers: proportional and time delayed. Each has its pros and cons, depending on the specific tow situation.
While this trailer deck is large enough to carry a full-size car or truck, its wheels, tires, and axles are not stout enough for such a load. A common load rating for an axle such as this 3,500 pounds. Remember that the load includes the weight of the trailer plus the weight of cargo. Trailers such as these are more appropriate for lighter vehicles such as UTVs, quads, and dirt bikes.
When choosing a trailer to haul a large vehicle such as a sandrail, Jeep, or truck there are several styles available with varying load ratings. Deck surfaces can be open, or filled with aluminum or steel sheet, or with wood planks. Metal decks typically last longer, but a wood deck is a more tolerable work surface in the hot sun. Trailer rail styles also vary, and may be added to increase the chassis rigidity. Note also that the fore/aft axle positioning can vary and is important to consider with respect to the loaded vehicle weight and positioning to achieve good balance and proper tongue weight on the tow vehicle.
Submersing your trailer in the lake? Water contamination is probably the number one enemy of axle bearings. The guys at Lewis Hitches mentioned that what often kills the bearings is not as much the water egress from weekend to weekend, but rather the time the water sits inside the hubs over the off-season and starts the corrosion process inside the hub. Hubs that offer external grease zerks can help prolong bearing life, however pumping too much grease into the hub can push it past the seal and contaminate the brake shoes or pads. Even with this type of hub, the bearing assemblies should be torn down and freshly greased at some service interval based on mileage and use.
Trailer axle failures are not uncommon. You'll spot the broken trailers along the highway with missing or shredded tires, damaged wheels, or more serious axle or brake failures. The large majority of these can almost certainly be attributed to poor axle maintenance and/or overloading of the trailer.
Trailer tires should also be chosen for their load rating. It is certainly possible to install passenger car tires on a heavy duty trailer and stay within the load ratings. However, there are tires designed specifically for trailer use and designated as `ST' type. These tires typically have stiffer sidewalls to reduce sway and tread designs meant to help a narrower tire run cooler and last longer in a trailer application where the tires are neither driven nor steered. `ST' rated tires have a maximum speed rating of 65 mph.
Trailer tires should always be inflated to the maximum pressure printed on the tire sidewall. The most common cause of trailer tire blowout is heat due to under-inflation. A small leak that causes the tire to deflate can go undetected much more easily on a trailer than on the car or truck you're driving. If you blow a tire on a tandem axle trailer, it is often a good idea to also replace the second tire on the same side of the trailer as it was probably overloaded when the first tire blew.
Small trailer tires can work fine for very lightweight trailers and loads. However, their smaller bearings will be more sensitive to overloading and their small diameter means they turn considerably faster than a full-size tire. Ensure that the hubs are well lubed with a quality grease.
Properly securing your precious cargo is just as important as the trailer connection to your tow vehicle. Consider that the trailer will bounce and move about, and transfers that action through your tie-down straps or chains. When slack occurs, hooks can come loose and exit their attachment points, possibly yielding ugly results. Ideally, all straps should use latching hook ends that remain fully captive even under slack conditions.
There is much debate as to whether vehicles should be secured to trailers by the axles or by the chassis. Strapping or chaining a vehicle to the trailer at the axles keeps it clamped tightly to the deck with only the vehicle tires as a "squish" point. The body is left to move about freely on top of its suspension. Straps should be run in a straight line to the end attachment point on the trailer, but not run over or around any structure such as has been done at the end of the trailer shown here. Synthetic straps offer great tensile strength but can tear when abraded against a surface.
Strapping a vehicle down by its chassis allows you to compress some of the suspension travel, and thus, reduce the amount that the body sways on top of the trailer. However, trucks typically have a good bit of suspension travel. When the trailer hits a bump in the road and compresses the suspension on the trailered rig, the chains or straps may go slack if hooked to the frame. The best method is to strap the axles and supplement with chassis straps if needed. Additionally, it's usually best to trailer a vehicle with it in low gear (manual) or in park with the E brake set.
Here's an example where a lightweight moon buggy was strapped down on a fifth wheel trailer using racheting straps. The straps were secured around the front and rear suspension links next to the frame link mounts. However, the straps are routed over the steel corner of the trailer, causing a point of abrasion on the strap. If such routing is necessary, protect the strap with a rag, piece of carpet, or cardboard placed between the strap and the trailer corner. As a side note, never use a winch cable as a primary means of securing a vehicle to a trailer. The tension placed on the cable as the vehicle is trailered can shock load and damage the internal planetary winch gears.