Here's a plug for…

The SAE J560 (black or green) plug has been used since 1951 to power the trailer functions: Ground, Side Marker Lights, Left Turn, Brake, ABS Power, Right Turn, and Tail/License per Federal Motor Vehicle Safety Standard (FMVSS108). This Standard includes definition of vehicle lighting, signaling, and reflective markings. The equivalent Canadian Standard (CMVSS) has required daytime running lights since 1990. This is not a US requirement.

SAE J560 dictates the common pin position for use with a green extension cord, but does have alternate wiring options, like those which tie the brake lights to the turn signals on the trailer. These things can be accomplished in the aftermarket.

The ISO 3731 (yellow plug, yellow cover) is an auxiliary seven way that has been in use since 1980. The optional functions are extensive, and include items such as: Ground, ABS Fault indication, Reverse Lamps, Control Ground, Ignition Lock, and Rear Fog Lamps, or any other auxiliary circuits. There is no common pin position.

The pins in each plug are positioned such that J560 and ISO3731 cannot be accidentally switched. That is to say, each cord will only attach to the proper mating plug.

Many newer model chassis today have a Pre-trip Switch which turns power individually to the J560 lights on the trailer to verify that they are operational. This saves the driver, many trips back and forth from the cab to trailer turning on the individual switches during their walk around. The Pre-trip Switch does not include the functions wired to the ISO 3731.

FMVSS121 applies to air brakes. Trailer brakes are pneumatic, so neither plug deals with the brakes, just the signals associated with the brakes (lights and ABS power).

Defeating the design

Winter fronts can increase the aerodynamic characteristics by directing ram air around the hood. Additionally, some of them look great, even in the spring and fall. But are they needed in these months?

Without the winter front, the engine coolant remains cool resulting in a cold heater core. The design intent of a winter front is to restrict cold ambient air flow under the hood, increasing the temperature in the engine block. The result is restricted air flow through the radiator, power steering cooler, fuel cooler, etc. depending how the OE configures the design.

However, we need to consider that the charge air cooler requires ambient air to be efficient, regardless of temperature. The small openings affect performance, plus increasing stresses on the cooler. The temperature delta from negative ambient to 400 degrees intake, can crack the cooler via thermal fatigue. This can create leaks beyond manufacturer recommendations, ultimately affecting fuel economy and performance.

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The front can also cause mechanical stress with the engine fan, moving from loaded to unloaded areas as it rotates. The cooler is generally designed to reduce temperatures to approximately 40-degree F above ambient, so the restricted air flow reduces the cooler’s effectiveness.

The winter front should only be used on a limited basis in extremely low ambient conditions.

Snap, Crackle, Pop...

Most OE’s offer auto reset mechanical circuit breakers as an option to fuses in the power distribution box. For a few more dollars, the driver can rely on these breakers to protect the circuit from an overload.

When a fuse blows, the circuit remains cold until it is replaced. Certainly, there is more effort with finding the blown fuse and replacing it, especially if there are multiple power distribution boxes. One of the ‘benefits’ of a fuse is the finality of the failure which forces the operator to think about what caused the problem, because they do not want to have to replace it again. However, there is risk associated with increasing the size of the replaced fuse as ‘fix’, which could overload the wire, causing a thermal event.

When an overloaded circuit pops the breaker, it must cool before reconnecting the circuit. The breakers use contact points, typically made from precious or semi-precious metal). To resolve the problem, the device that overloaded the circuit must be removed, however there is no guarantee this step will occur (especially on the road). Most customers prefer breakers because they are simpler. However, if the points continue to open/close, and the load that causes the issue has not been removed, the chances of points welding increases. A welded circuit could cause a thermal event in the circuit it was designed to protect.

Two OE’s that I am aware of have designed Poly Switches into some of their chassis circuits. The poly switch serves as an over current protection alternative, using carbon black vs. points. As it heats up, it eventually opens the circuit and will close when the temperature drops, so it acts much like a common breaker, but has no points to fail/weld, thus is a much safer design.

All OE’s use 5 amp fuses on the limited circuits since they are more susceptible to overload.