Multiplexing Multiplexing is using one electrical wire to perform many operations. A new automobile, without multiplexing, can contain as many as 2,000 wires. A driver’s door may have up to 50 wires. Multiplexing can reduce the same door controls to just four wires. The additional cost of electronics at both ends of the cable is causing a slow change to multiplexing. It is not easy to repair a conventional auto wiring problem today. Just look at the manufacturers’ wiring diagrams and you will agree. Wire harnesses, in early years, had only a few wires inside each jacket. Today, space for the large wire bundles is causing a problem. We can hardly imagine the car of tomorrow. Manufacturers are talking about side air bags, navigational equip- ment, updates of anti-theft devices, win- dow and seat heaters, and additional smog controls to name a few. For safety, some are starting to lock out an air bag if a small child is in the seat. With multiplexing, low power signal wires will connect to a destination elec- tronics chip. The chip may tell a motor to run or will tell a turn signal to flash. Many functions can be accomplished with one signal wire instead of a sepa- rate wire for each. If a light burns out, a signal can be returned, on the same wire, to a central control and then send the signal to a dash chip on a single wire. The dash chip can then turn on an alarm informing the driver that a light is out. A power and ground wire is required for each processing chip. The ground wire can function also as a ground wire for the signal. Mercedes and BMW already have some multiplexing. Additional test equipment for multiplexing circuits is also a consideration of cost. The microchip has changed our lives. We find them in our homes, offices, and in our cars. To counteract multiplexing, some manufacturers are attempting to remove some wires or change the wires to a smaller gauge. However, wiring harness- es are complex and expensive to build. The cost of electronics is dropping every day. Multiplexing will change and encourage many new functions in the automobile. With the proper test equip- ment, repairs will be much easier than tracing many wires. Larry Wilhelm, formerly of ACE Electric, Columbus, KS.