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What Options Do I Have for Testing My Trailer?

Home » Blog » What Options Do I Have for Testing My Trailer?

Nov 13, 2023 | News

The electrical systems found in semi-tractor trailers are getting more sophisticated, including refrigeration and tire inflation systems in addition to traditional signal lights and braking systems. The trucking industry is also moving toward more efficient 24 and 48-volt electrical systems. Working with the correct trailer tester makes working with intricate trailer electrical systems more manageable. Here is more information about various trailer testing options to help you make an informed decision when purchasing trailer testers for your shop.

Diagnostic Tools for Trailer Electrical Systems

A trailer tester can range from a simple, specialized tool to a complex diagnostic system. Basic plug-ins and universal testers are helpful for quickly testing electrical systems, making diagnosing standard electrical systems easier. More versatile tools like multimeters and oscilloscopes provide highly detailed information for diagnostic situations where more data is needed to find a problem.

Plug-In Circuit Testers

The most straightforward trailer tester solutions are simple devices that plug directly into the trailer’s wiring harness. These devices are easy to use and provide a quick way to identify which of a trailer’s circuits are not working. While these testers are easy to use, they specialize in specific system architectures. Each of these testers is designed for only one type of circuit connector, such as a 7-way spade pin or 6-way round pin connector. These tools are helpful in shops that regularly diagnose large numbers of standardized electrical systems.

Universal Trailer Testers

Universal trailer testers are much more powerful than plug-in testers. These tools give technicians more data than simple plug-in testers. Universal testers provide information about a circuit’s wattage and load capabilities. Technicians can use universal testers to find problems a plug-in tester may miss. While a plug-in tester will show you whether the circuit closes, a universal tester can also tell you if it’s carrying enough power to do its job.

Another advantage of universal testers is that some models can test a trailer’s pneumatic and computer systems. Trailer testers like these can read and interpret error codes from a truck’s onboard computer system. Some can also test the pressure in a trailer’s brake system. This data gives technicians more information while combining several diagnostic tools into one device.


Testing a trailer’s entire electrical system is not always necessary. In these cases, technicians may only need to test the subsystem or components causing the problem. Multimeters allow technicians to isolate and test individual components’ voltage, resistance, and other properties. Technicians can use a multimeter to test subsystems like the anti-lock brakes system or individual components like lights and transformers. This eliminates the need to find system faults by addressing the suspected problem and re-testing the entire system. Eliminating this sort of trial-and-error approach saves repair technicians time and money. Multimeters are also helpful because of their small size and portability.


An oscilloscope is among the most powerful of electrical diagnostic tools. Oscilloscopes combine the numerous diagnostic features of a multimeter with a visual record of system performance. These tools visualize changes in the system’s voltage and current while the circuit performs its functions and interacts with other systems. This can help technicians more easily identify intermittent problems and sources of electrical interference.

Other Trailer Testing Equipment

David’s Heavy Duty Tool Sales offers many other tools that help diagnose electrical problems. Fuse savers and relay bypass switches don’t test electrical systems directly but help make the diagnostic process easier. Repeatedly swapping fuses and activating relays takes time. These tools help technicians save time by making these tasks simpler and helping them avoid repetitive steps.

Fuse Savers

Short circuits and power surges are common problems in electrical systems. Fuses are designed to break first when an electrical system experiences too much load. This protects other components from damage, but replacing a blown fuse between every diagnostic test wastes time and money.

Fuse savers solve this problem by allowing a technician to replace the fuse with a reusable device that allows testing on the circuit without stopping to swap fuses. Some models also make an audible noise to tell technicians exactly when the fuse would have failed. This information can make diagnosing electrical system flaws much faster.

Relay Bypass Switches

Another helpful tool for diagnosing electrical systems is a set of relay bypass switches. When testing subsystems like fuel pumps and cooling fans, these switches let technicians bypass the truck’s control systems. This allows one technician to test electrical components without needing an assistant to operate the controls that run these systems under normal conditions.

Find Trailer Testers at David’s Heavy Duty Tool Sales

Whether you’re equipping a new shop or expanding an established truck repair service, David’s Heavy Duty Tool Sales can help you find trailer tester equipment. We carry a variety of testers and related tools, from simple plug-in testers to versatile universal testing systems. Visit our website or contact us today to find trailer testers that meet your shop’s needs.