Chassis multiplex electrical systems are found on almost all commercial trucks, fire apparatus and ambulances. They tie together the control systems for engines, automatic transmissions, antilock brake systems, instrument displays and many other components to allow quick and reliable operation without requiring a mass of tangled wires or a block of mechanical relays.

One complaint about multiplex electrical systems in the past was that they were difficult to understand, difficult to install and difficult to troubleshoot. There also was no common system between manufacturers, which meant that every time a fire department went out for bid on a new vehicle, it faced the possibility of having to deal with a new system.

That has changed over the past few years as the Weldon V-MUX multiplex electrical system has been adopted by more than 40 fire, rescue and ambulance manufacturers. Currently, the system is available on apparatus built by Crimson Fire, Ferrara, Smeal and several dozen others. Fire apparatus chassis built by Spartan Motors also are standard with the system, as are ambulances built by Braun.

"One of the reasons the system has been so widely adopted by manufacturers and users alike is that it has taken a lot of the mystery out of multiplexing," says Peter Luhrs, director of V-MUX for Weldon. “The key components are several electronic modules mounted in various areas of the vehicle — in older electrical systems they would have been called junction boxes. Like junction boxes, they provide easy access for connections and troubleshooting.”

According to Luhrs, the system’s display and control unit add to its popularity. This flat panel unit is mounted in the cab and can be used by the driver, officer or both. It contains switches and displays for a variety of functions, including emergency light activation, gauge displays, air-conditioning and heating controls, and many others. It even can automatically display the view from a rear-vision camera when the vehicle is placed in reverse.

Unlike some other systems that are based on sensitive components typically used in personal computers, the V-MUX system is designed to work in a more rugged truck environment. Before introduction, the system was subjected to the tough temperature, shock, and vibration tests prescribed by the Society of Automotive Engineers to ensure it would survive in vehicle applications. As an example of the severity of these tests, V-MUX can operate in temperature extremes ranging from −40° to 185°F without problems, conditions that would cripple most computers.

If problems do occur, troubleshooting is made easier with both on-board and plug-in diagnostics. The Vista III display can give technicians information on a variety of problems, and a separate diagnostics kit allows them to further isolate and identify specific problems.

And if departments ever want to alter the system or add components in the future, V-MUX can readily be re-programmed or re-configured to handle the changes.

For more information about Weldon's V-MUX multiplex electrical system, call 800-989-2718 or visit www.v-mux.com.