Shovelhead Wiring

Harley-Davidson electrical systems were much more mechanically conventional right up to the early Evolution models. Although there were numerous wiring and component variations between years and models and model accessories, electrical systems and wiring were fairly basic.

These earlier systems consist mainly of:
– A battery and battery cables
– 30-amp main breaker
– Two to four 15-amp breakers
– Ignition switch
– Charging system or generator
– Voltage regulator rectifier
– Starter relay and/or a starter solenoid
– Starter motor
– Turn signal flasher (later, a turn signal module)
– Points or electronic ignition and ignition coil
– Lighting, signals & indicators
– Brake switches, neutral switch, oil pressure switch, and handlebar switches.

With the battery powering a main breaker and ignition switch, functions are powered off of separate 15 amp breakers. Most components need to be both powered and grounded in order to complete their corresponding functions.

CAN BUS systems of today function a lot differently

CAN (Controller Area Network) and BUS refers to a network with a central control module (or computer) that acts as a central computer hub. It is separate from the motorcycle’s ECM. This central computer is the hub and a single wiring harness connects the computer to its sub systems, allowing them to communicate. With this single wiring harness, different functions can piggyback on each other. One wire can perform multiple tasks. This greatly reduces the amount of wiring needed in comparison to the previous point-to-point electrical system.

Various sub-systems have their own micro computer command stations that are constantly talking back & forth with the central computer which monitors everything. If there is a failure, the central computer can automatically shut down that particular system. This eliminates the need for a fuse box with up to a dozen fuses. So, if there is an electrical malfunction like a dead short, the computer will shut down an isolated system and send an error code message to the speedometer display. This is a considerably different outcome than a point-to-point electrical system where a dead short would blow a fuse or trip a breaker.

Sounds good, right? Well, some of us older wrenches get really anxious around computers. A lot of us still prefer dealing with generators, points, breakers, test lights, and the occasional smoked wire.

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