Who Needs a Second Connector?

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For all the hype about multiplexing (carrying multiple signals across a single wire) the real payoff for truckers has yet to come. For a typical tractor-trailer connection, you still need to use the blue or auxiliary circuit to control or monitor trailer functions, if not doubled-up cabling by way of another cord beside the standard seven-way J560 cable. And the tractor-trailer interface trucking industry groups agreed last summer to support as a standard-power-line carrier technology called PLC4Trucks-is relatively complex and not yet widely available.

If a PLC4Trucks solution seems a distant prospect, a new multiplexing product from Hendrickson Trailer Suspension Systems represents the here and now. Using the standard seven-way J560 connector, it offers eight additional circuits between tractor and trailer, one of which is programmed to monitor trailer ABS status and report via a dash warning light. It means an end to using the blue auxiliary circuit to control or monitor trailer functions. And for some fleets, it means an end to doubled-up cabling by way of a second connector.

It’s available today, off the shelf, which in itself makes the system somewhat unique.

The optional twist: portable multiplexing! You can buy a control module that plugs into the tractor’s cigarette lighter (or connects to a CB post), thus avoiding the need for hard wiring and making tractor/trailer compatibility issues easy to resolve. It can move from tractor to tractor, connecting to any properly equipped trailer.

Called Control Link, the system is the result of a new company division, Hendrickson Vehicle Control Systems, headed by Mark Waltz, working in partnership with Air Weigh Systems. Hendrickson engineers redesigned Air Weigh’s existing Wire Link multiplexing product (changing from negative to positive switch grounds, for example), and Air Weigh has become the joint effort’s manufacturing arm. As Wire Link, it’s actually been in use in thousands of trucks since 1995, so it’s not an unproven product.


The standard Control Link system has two basic parts: the Powered Vehicle Module, hard-wired into the tractor, and the Towed Vehicle Module, hard-wired into the trailer’s electrical system. The optional Towed Vehicle Controller (TVC) is the portable version of the tractor module. The hard-wired modules are about six inches long, three wide, and one inch thick, and weigh all of 12 ounces. The portable unit is half again as big and about double the weight, with monitoring lights and switches built in. It can be mounted on the dash or hand-held.

In either combination, the system provides four circuits for communication from tractor to trailer, and four others from trailer to tractor. One of the trailer circuits will likely be used to monitor trailer ABS status (required in the U.S, and effectively in Canada, by March 2001), while others could monitor door alarms, reservoir air pressure, reefer temperatures, etc. The four circuits from the tractor might be used to control trailer lift axles, air-suspension dump valves, interior dome lights, liftgate power, backup lights, or what have you. In either case, you choose the four devices you want to control or monitor, and the beauty of it is that your existing J560 connector doesn’t change at all.

Waltz says, incidentally, that there could easily be another eight circuits (four in each direction) if required, by the simple addition of a second “brick” or module in the line.

The system uses industry-standard wiring harnesses, works on the basic 12-volt standard, and meets or exceeds all industry, SAE, TMC, and NHTSA requirements. It includes a self-diagnostic light display with flash codes to show low voltage, internal failure, or transmitter failure.

The benefits of the Control Link system are many, says Mark Waltz. For the driver, it means he can readily stay in touch with what’s going on in the trailer (reefer temperature is an obvious example). It also gives him easy control of trailer accessories with the touch of a switch and reduces the number of unnecessary trips in and out of the cab.

The chief benefit of the portable TVC is that all new and old tractors can operate with new trailers. There’s no need to dedicate tractors to new trailers. The control unit has a flexible coiled cord that will stretch to about 12 feet, meaning the driver can use it outside the cab and observe that the axle is lifting, the liftgate lowering, or whatever.

For many fleets, however, the real gain should be the absence of an awkward second J560 connector system. “If you ask us who is our competition, it’s really the second connector,” says Mark Waltz. The other competitor is only one in theory, namely the PLC4trucks system being developed by a Freightliner Corp.-led consortium. But that’s not available now, and Waltz says it likely won’t be needed for another 20 years. He raises the point that the sophistication of many trailer mechanics may not be up to that kind of complexity at present anyway. The Control Link system, on the other hand, is dead simple.

Marketing the system has been made much easier by higher production volumes and thus a recent major price reduction (it’s now likely to cost between $250 and $350 for a complete hard-wired tractor and trailer system). “We’re extremely competitive now [compared to the second-connector option] and the OEMs are now quoting the fleets on our product,” says Waltz.

The emergence of the portable TVC has also made the marketing task easier, because it eliminates the difficulty of co-ordination between tractor and trailer OEMs, and allows trailer makers to sell the complete system as a kit.

Control Link is available now, ready to ship, in both hard-wired and portable versions.

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Rolf Lockwood is editor emeritus of Today's Trucking and a regular contributor to Trucknews.com.

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