Wayne Cook
July 1, 2009

Whether you’re restoring a classic Mustang, building a restomod full of modern technology, or assembling a Factory Five Roadster, you’ll have to make some important decisions about the wiring in your project. Wiring can be one of the most complicated jobs encountered during the course of an automotive restoration or custom build. It requires the careful routing of numerous control wires and power leads to and from switches, and the various other electrical components within the chassis and body. The wires are bundled into cables that must be carefully hidden to achieve a clean and sanitary looking installation. On a restoration project, sometimes the factory harness will be serviceable and sometimes it will not, while those starting from scratch are doing just that. Before you go forward with the electrical aspect of your next project, you should be aware that a new choice for vehicle wiring exists in the form of the Littelfuse ISIS Intelligent Multiplex Wiring System. The ISIS arrangement is a modular micro-controller–based automobile electrical system than can replace or augment a conventional wiring harness. It uses a centralized command or “hub-and-spoke” arrangement to greatly simplify electrical wiring projects.

Rather than having a complete and separate circuit for each and every vehicle electrical function, such as headlights or turn signals, the ISIS system uses a Mastercell input unit that communicates to a remotely located Powercell through a single small connection. Electrical switches in the car are wired directly to the Mastercell unit. These switches are all ground side controlled and carry low-current only. When a switch is activated the input is transmitted from the Mastercell to the Powercell via a CANBUS connection. The Powercell then executes whatever command the Mastercell provides. A typical car installation might have two Powercells, one for each end of the car. However, the Mastercell can command as many as five Powercells, each with ten possible fused outputs, for a total of 50 functions that can be controlled by a single Mastercell. This capability is very useful for large vehicles with numerous requirements such as a motorhome or a boat. Let’s have a look at the individual components of the ISIS system and see just what the potential advantages are.

Besides simplicity, one of the big advantages of the ISIS system is ease of installation. The wiring of a vehicle can be a big part of the project and can take many hours to complete. However, with the new ISIS system you can cut that time dramatically and you don’t need to have a lot of past wiring experience to complete a clean installation. As well as ease of installation, enthusiasts will appreciate the approximately 40 percent weight savings realized using the ISIS arrangement. Another advantage is safety. As we just mentioned, the low-voltage and low-current design for switching and controlling electrical functions eliminates high-current wiring under the dashboard. This reduces the possibility of an under-dash electrical fire or overloading a dash switch. All inputs are ground-switched, further simplifying the electrical system. A low-current dash harness is available as an option, providing easy connection to all switches and gauge wiring.

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