The following wiring diagram depicts the Alfa Romeo 155 Starting and Charging system. Begin with detail illustration of the wiring diagram, you will find detail description and explanation of the starting and charging system of the vehicle. Alfa Romeo 155 starting and charging circuit are composed of one battery, starter motor, and alternator. The battery (12 V) is of the sealed type and does not required maintenance. The starter motor consist of a motor supplied DC power from the battery and command and engagement solenoid.
When the ignition key is rotated the voltage from the battery supplies the coils of the motor generating the electromagnetic forces which rotate the pinion of the motor itself. At the same time the solenoid is activated and works the engagement mechanism which engage the pinion in the crown wheel of the flywheel thus causing the crankshaft to rotate. The alternator charges the battery during normal rotation of the engine. The spindle of the alternator (rotor) which is forced to rotate by the crankshaft through a belt is supplied with the activation current which generates a magnetic field which induces an alternating current on the stator. This is then transformed into direct current by a bridge rectifier with diodes and sent to the recharge the battery. A voltage regulator incorporated in the alternator makes it possible to maintain a constant delivery of voltage (approx. 12 V) for all the fields of variation in loading and engine r.p.m.