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In order to safely slow down towing vehicles and trailers, brake controllers send the right amount of power to a trailer's set of brakes. See more truck pictures.

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Introduction to Brake Controllers

If you've ever gone roller skating at the rink with a large group of friends, you might very well have started a train. With everyone in single file and holding onto the person in front of him or her, the train continues in a circle around the rink. As long as everyone skates together at the same relative speed, the line will move along safely.

The group can't go on skating in circles forever, of course. So when someone needs to take a break, the best way the whole train can slow down at the same time is if the person at the front of the line sends a signal to rest of the skaters to slow down. This way, each skater stops at about the same time, avoiding any collisions. If the front skater had decided to stop on his own without letting those behind him know of his decision, the full force of the train's momentum would cause his fellow skaters to crash into him, creating a massive pileup and probably tripping up any nearby strangers.

You can think of a truck towing a trailer in a similar way. If you simply hitch your trailer up and head out on the road, slowing down becomes more difficult because of the extra weight behind your vehicle. Fortunately, most states require drivers to equip their trailers with brakes and devices known as brake controllers. When a driver presses on the brake pedal in his truck, the brake controller lets the trailer's brake system know how much braking power is needed to stop the trailer.

What types of brake controllers are there? How do you know how much power goes into the trailer's brakes? How are brake controllers installed? Read on to learn about brake controllers.


There are two types of brake controllers -- proportional brake controllers (shown above) and time delayed brake controllers.


Types of Brake Controllers

Although there are several different styles, we can divide brake controllers into two distinct groups -- proportional brake controllers and time delayed brake controllers.

Proportional brake controllers use a motion-sensing device to detect how fast the tow vehicle is stopping. The moment the driver applies the brakes, the brake controller applies the same amount of braking power to the trailer's brakes -- if the truck is stopping quickly, the trailer will stop quickly; if the truck stops slowly, the trailer will stop slowly. In a situation that requires heavy braking, for instance, a proportional brake controller will cause the trailer to stop at exactly the same time as the truck does. This type of brake controller provides the smoothest braking, and because both systems are doing the same amount of work, it reduces the amount of wear on each vehicle's braking system.

Proportional brake controllers are also known as pendulum brake controllers because of the way they sense motion. These devices use the position of a pendulum as a motion-sensing device, and drivers typically need to calibrate them before using them. When the vehicle is on a level plane and the pendulum is pointing straight down to the ground, the brake controller doesn't sense any motion and won't send any signals to the trailer's brakes. When the vehicle moves, however, the pendulum points toward the rear of the vehicle. As soon as the vehicle brakes, the pendulum swings forward. Depending on how far the pendulum swings, the brake controller sends a degree of power to the trailer's brakes.

Time delayed brake controllers, on the other hand, provide a pre-determined amount of power to the trailer's brakes when the truck stops. The power is set beforehand by the driver and depends on how much trailer weight he's towing. A delay will always occur when the brakes are pressed; however, a sync switch allows the driver to adjust the length of the delay. Time delayed brake controllers put more wear on braking systems, but they're less expensive and easier to install than proportional brake controllers.

Brake controller monitors tell how fast a vehicle is going, show how much braking power the system is applying to the trailer and whether or not there are any warnings.


Brake Controller Monitors

Sometimes simply hooking up a brake controller to your trailer isn't enough reassurance. It helps to know how much brake power you're applying during a stop or whether the trailer brakes are even functioning at all. Brake controllers almost always have some type of monitor built in, which, if placed correctly -- often under the instrument panel, near the driver's right leg -- is easily viewable from the driver's seat.

Digital display screens show the voltage delivery going from the brake controller to the trailer's brakes. The more you press down on the brake pedal, the more power will go toward the trailer's brakes; if you give the pedal a softer touch, less power goes to the trailer's brakes. The brake controller monitor reflects the amount of pressure and power you're applying to the brakes. Brake controller monitors help you make sure your trailer is properly connected and will notify you of any electrical problems that could put you in danger.

As technology improves, newer brake controllers, specifically electronic ones, offer more monitoring options. Some models come with LCD screens that give specific, continuous diagnostics and important warning signals to drivers. Often, displays are customizable, with language options in not just English but French and Spanish -- some even offer color choices.

Installing a brake controller usually consists of finding the right place to mount the device and hooking up the right set of wires.


Installing Brake Controllers

Installing a brake controller is a fairly easy task. The first step involves simply mounting the brake controller in an area that is easy to access. Most people choose to place it under the dashboard and directly above your right leg; this keeps the brake controller in view, where you can monitor any potential problems.

Brake controllers typically come with a four-wire configuration, which can be hooked up to the braking system's wiring. The four separate connections are:

  • Trailer feed - supplies brake power to the trailer connector
  • Ground - connects the brake controller to a negative, grounded source
  • Brake switch - the wire that transfers power once the brake pedal is pressed
  • Battery power - supplies power to the brake controller

If you're not comfortable with bundles of wires, you might want to have a trained professional take care of your brake controller installation; however, if you know what you're doing and follow the directions provided by the device's manufacturer, installing a brake controller shouldn't be a problem.

For lots more information on braking systems and towing, see the next page.

Lots More Information

Related HowStuffWorks Articles

More Great Links


  • Dyer, William. "Combination brake controller and monitor for an electrical braking system for trailers." July 13, 1993. (Sept. 30, 2008)
  • "Trailer brake controller installation and types." (Sept. 30, 2008)
  • Southwest Wheel Company. "MaxBrake brake controller." 2007. (Oct. 5, 2008)
  • "Installing a brake control on a vehicle equipped with a factory towing package."2005. (Oct. 5, 2008)