But why care? It’s just an out of service…fix it and keep rolling… right? Well that will work for awhile and until the annual renewal for your motor carrier insurance. Then you’re going to feel like you got hit on the blind side by a NFL defensive end when your rates double, triple, or you get altogether “sacked” by your insurance company.
Checking and maintaining a properly functioning trailer e-brake is simple if you understand the system, and know how to test it. We know many drivers that understand the system, but not how to test it. There are 3 basic components: 1) The trailer battery, 2) the quick release trailer relay, and 3) the cable and pin that connect the relay to the truck. The concept is simple. The trailer relay will apply power to the trailer brakes, if the pin is pulled out. This is an important emergency function that will stop a trailer if it should become disconnected from the power unit. To test the system pull the pin out of the relay and try to drive a few yards. If the brakes apply stopping the truck and trailer, without using the truck brake, the system is working. However there’s more… what most drivers forget is the trailer battery is part of the system and if the battery is dead your system will fail a DOT inspection.
The wiring harness between the truck and trailer sends power constantly to the trailer, this is the circuit that powers the winch, and charges the battery. To isolate the e-brake system under battery power, repeat the test above, but also disconnect the pig tail connection between the truck and trailer. Now the only power source to engage the trailer brakes when the relay pin is removed is the trailer battery. If the system works with the pig tail connected, but NOT when the pig tail is disconnected, the trailer battery is dead.
This simple test should be part of every pre-trip inspection… that’s the way to keep rolling, and out of the grasp of the those DOT defensive ends.