Today’s trailers are more power hungry than ever. The pigtails that establish an electrified link between tractors and trailers are being called on to support everything from reefer batteries to communication systems.

The demand on the J560 connector’s auxiliary pin even continues to grow. “Everybody acts like it’s a public domain,” notes Bruce Purkey of Purkey’s Electrical Consulting, referring to the way that those who install auxiliary equipment are tapping into the pin’s power.

But the demands don’t end with auxiliary equipment. That connector also needs to deliver 12.5 volts and 10 amps of power to support the trailer’s Antilock Braking System (ABS).

“The tractor supply voltage has a significant influence on the voltage available to the ABS,” notes Bob Rudolph of Haldex Commercial Vehicle Systems. If the voltage falls short, the system will not work as designed, leading to flat-spotting trailer tires, failed roadside inspections or even collisions. And one in four roll stability systems are not functioning because of a lack of voltage at the blue auxiliary pin, Rudolph adds. “There is no redundant backup in these cases.”

It makes the ongoing inspections of the wired connections particularly important – especially since the maintenance efforts often fall short.

“Rarely do you ever see anybody check the seven-way cord on the tractor side. Everybody assumes the tractor is in good shape,” Purkey notes.

Even though TransAm Trucking was inspecting the connections for damage, it ran into challenges of its own.

A simple LED tester had been the tool of choice, notes shop manager Jim Ohlmeier. If the bulbs lit up, the connections were considered to be sound. But the fleet was still baffled by failing starter batteries on its reefers.

“The issue was not with the charging system, but with the voltage we were supplying, or in some cases, not supplying,” he explains. “The problem with these types of tests is they take minimum voltage and amperage.”

“The simple LED trailer cable tester may show ‘all systems are go’ on the trailer connector, but until you add sufficient load to the tester, you will never find the hidden voltage drop, or the corroded or damaged terminal,” he adds.

A more sophisticated tester has since shown that voltage drops on the fleet’s equipment ranged from 0.9 volts to 3.9 volts.

As important as the auxiliary pin may be, Brad Van Riper of Truck-Lite also suggests that the remaining wiring can’t be ignored. Even LED bulbs require a specific amount of voltage before they will deliver an expected brightness. If the power supply drops below 11 volts, the lighting may actually be less visible. “Twelve-and-a-half volts will make everybody happy and your vehicle a lot safer,” he says.

In many cases, power issues can be traced to something as basic as the gauge of wiring since the amount of copper will affect the draw of the current. Even though most truck manufacturers supply new vehicles with green pigtails (equipped with an eight-gauge, two 10-gauge and four 12-gauge wires), 60% of the cords sold in the aftermarket only have a single 10-gauge wire and six 12-gauge wires. It raises an important question: will the black replacement cord and its thinner wires provide sufficient voltage? “The chain of the electrical system is only as strong as the weakest link,” Van Riper says. “You need to start with enough copper and a good harness design to supply the loads you need.”

The challenge extends to the trailer’s own wiring harnesses. While 14% of trailers are equipped with a main wiring harness that has a single eight-gauge wire, a pair of 10-gauge wires, and four 12-gauge wires, 76% are equipped with a single 10-gauge wire and six 12-gauge wires, Van Riper says. (The remaining trailers included split mains or another type of wiring harness.) “And as the cost of copper increases, there is an attempt to lighten the gauge even more.”

Other voltage-related challenges come down to issues such as poor connections, overheating wires, the build-up of moisture or corrosion. Then there are the worn and distorted terminals, corroded terminals, corroded wires, open fuses and circuit breakers, or challenges with the tractor ground circuit.

“A significant amount of damage can occur in the wiring before they ever become hard faults,” Rudolph observes.

It’s why maintenance teams need to be aware that every connection counts.