It's an old problem in America's prisons and schools, but overcrowding on a truck? With abundant accessories, cab fixtures and capabilities, the wiring systems that carry data throughout a medium-duty vehicle these days can often become cramped and unmanageable.
Multiplexing allows for a fewer number of internal data wires, as certain single wires can be programmed to carry different loads of information at different times. The key to multiplexing is allowing for separate data to be transmitted, making sure that only the message that needs to be sent is the one occupying the line. The folks at International Truck know a lot about multiplexing because they have developed their own proprietary system.
Hardware manager for International, Brian Marts, explains the reason behind the transition to multiplexing. "What's really going on is you've got more and more electronic controllers on a vehicle. One thing that was happening was you would have gigantic bundle sizes of potentially hundreds of wires," Marts says. "That all became very difficult to string and package around the space requirements on a truck.
"What you have with multiplexing," he continues, "is all of your modules communicating on the same protocol."
HOW, WHEN, AND WIRE?
Sound like a lot of engineering jargon? Here's where the benefits come in for maintenance: "What's nice about (multiplexing) is you only need one tool to access each of those modules," Marts says. "It used to be—in the old times—you would have to have more than one service tool… very much like a skyscraper where every floor has its own unique number, same thing with each of the modules. So now you've got the power to basically query anything in the electrical system that is connected to that."
Another advantage in terms of maintenance is the way in which multiplexed systems often have the ability to self-diagnose problems. This goes back to the on-board diagnostic system in a vehicle: if a command goes out and gets no response, it can send back a maintenance alert to the database.
"Because we put more electrical content in, there is a potential downside for people because it can be kind of hard to understand how the pieces work," Marts says. "So as things get more sophisticated, you need training to understand the new material. We offer the International Service Information System (ISIS)."
In the form of a CD-ROM, ISIS includes service manuals and circuit diagrams, as well as background technical information on almost all International models. According to their website, the ambitions of ISIS are for it to be "a single volume in what will become an encyclopedia of service data delivered electronically to every service bay in the International network."
MANUFACTURERS DO THEIR PART
New systems mean a change in operations from a manufacturer perspective. For Grote Industries, multiplexing created a whole new venue of additional testing procedures for their lighting products. Walt Bronson, product manager, turn signal switches for Grote Industries explains the preventative testing regimen:
"All product designs are subjected to a minimum of three levels of validation testing and analysis before production shipments begin," Bronson says. "On-vehicle road testing will also be completed at each validation series to ensure actual performance and drive-ability of the product."
Truck-Lite also believes that the easiest way to track and deal with failures is by preventing them altogether. "With the development of LED light sources, it is far more cost effective to develop lighting products that can likely last the life of the vehicle, rather than work on proactively determining when the failure will occur," Van Riper says. "Truck-Lite has registered the phrase ‘Fit and Forget' as an example of how long these new extremely robust products will last."
Still, no matter how informed a supplier is in the manufacturing process, it is still a good idea for techs to be prepared for the worst. Most of the failures in lighting products, according to Grote's chart on the subject, seem to come from improper installation, storage or external concerns (like weather). Tracking and replacing these failures will keep trucks out of the shops and on the roads.