Let's face it, wiring a customized classic truck can be one of the most daunting aspects of a build for the uninitiated or even the more-able hobbyist. When do I use a relay? What gauge wire should I run? What size fuse should I use? Why do I keep blowing fuses? What happens when I run out of room on my fuse panel? These are all problems I've had in the past and questions that have left me scratching my head and searching for answers. Fortunately, there are a number of companies that provide not only technical support for us homebuilders, but also provide a plethora of products that solve each and every one of these problems. From complete wiring harnesses to extra fuse panels to individual relays to technical literature, the answers are out there to simplify and solve your wiring woes. But one thing that has always been a constant when it came to wiring a truck was the need for a large, unencumbered wiring harness. A standard 16-fuse system in the past entailed wiring each individual load to the respective switch as well as to the fuse panel. This meant that with vehicles with numerous items at the rear, such as stereo equipment or air ride suspension components, lights and EFI fuel system requirements, suffered from a bulky set of wires that passed three-quarters the length of the vehicle. That usually left the upholsterer with a large clump that had to be hidden under carpet and upholstery, resulting in a rather unsightly and inaccessible wiring situation.

Well as we all know, the technology that trickles down from the big OEMs oftentimes finds itself lending a credible hand to our industry and this time that technology comes in the form of the ISIS Intelligent Multiplex System. An advanced, modular, solid-state, microcontroller-controlled electrical system that replaces or augments an existing traditional wiring harness, regardless of make, model, or year of your vehicle, the ISIS Intelligent Multiplex System, ISIS for short, simplifies electrical system installation and the installation of additional accessories, all the while providing flexible and nearly limitless control of your vehicle's electrical system. By employing a plug-and-play modular design, identical to that used in OEM vehicles, and computerized power distribution, ISIS reduces the amount of wiring needed using a hub-and-spoke strategy.

How it works
The ISIS system basically consists of two components, the Mastercell input unit and the Powercell control unit(s). The Mastercell input unit provides the system's intelligence and distributes instructions to the various Powercell control units via a CANBUS connection. Think of the Mastercell as the hub. Each Mastercell can manage up to five Powercells with each Powercell capable of handling ten nodes or outputs, allowing the system to manage upwards of fifty circuits, with the possibility of adding more Mastercell and Powercell units for a limitless system. The Powercell provides individual, built-in circuit protection (negating the need for a stand-alone fuse panel) and distributes the power to the vehicle's accessories. A typical installation would locate one Powercell at the front of the vehicle for lights, ignition, starter solenoid, windshield wipers, and other electrical accessories, while a second Powercell mounted in the rear would control the turn signals, brake lights, hazards, fuel pump, and level sender. Wiring the vehicle is dramatically easier since the wires no longer need to run all the way from the switch and fuse panel to the individual accessories (this is achieved via the CAN cable that relates the needed information between the Mastercell and the Powercell and then distributed by the Powercell to the related accessory).

The ISIS system allows you to control any part of the vehicle's electrical system in many different ways. You may program a light to blink as a turn signal or stay lit as a running light. Each mode of behavior is what ISIS calls a "personality." Custom personalities are possible or you may reconfigure standard personalities from the existing library to cater the system to your particular desires, such as controlling the brightness of your headlights using a fixed-pulse-width modulation personality to create daytime running lights. The personality description describes how the personality functions and the various states that are created during its function on the Powercell. These personality descriptions are stored in the Mastercell, which assigns them to the Powercell dynamically.

Communication between the Mastercell and the Powercell when a given type of personality is applied is achieved using one of four possible relationships: one-to-one, one-to-many, many-to-one, and many-to-many. One-to-one is a relationship where a single input on the Mastercell controls a single output on the Powercell. One-to-many means that one input on the Mastercell controls multiple outputs on the Powercell. A many-to-one relationship means that many inputs on the Mastercell controls one input on a Powercell. Last but not least is the many-to-many relationship where many inputs on the Mastercell control many outputs on a Powercell.

While all this talk about personalities, nodes, and relationships might start to sound confusing, keep in mind that the ISIS Multiplex System is designed to be a self contained unit in that unless a custom function is required or desired by the user, the system contains the proper personality for the majority of given vehicular requirements and is prewired accordingly. For example, switch input 11 and 12 are setup with a self-canceling turn signal personality and correspond with either the brown or violet wires on the Powercell. Hook these up to the lights and connect the yellow-and-black and the yellow-and-red wires from the Mastercell to the switch or existing turn signal lever harness, and the turn signals are ready to go. No flashers are needed and the personality allows the Mastercell to determine when to cancel the signal depending on a number of preprogrammed functions.

What the ISIS Multiplex System boils down to is basically a true-blue plug-and-play wiring harness. Wire each Powercell to its respective items, wire the Mastercell to each respective switch, connect power and the CAN cable, and you're off and running. No more untangling giant rolls of wiring or tracking down a short or other electrical malady throughout the length of the car under carpet and upholstery. With the short travel distances between the Powercell and its outputs and the Mastercell and its switches, the amount of wiring in a typical vehicle is decreased dramatically. This simplifies the job not only for the wiring guy but will also make you a little more popular at the upholstery shop since the trimmer will no longer have to hide that big clump of wiring running down the center of the floor. And cutting the time needed to install a complete harness means cutting down on labor costs, saving you a little bit of dough as well when it comes time to wire that new hot rod project.

SOURCE
Littelfuse, Inc.
www.isispower.com
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