Connections which can become corroded and cause trouble. Can't mention it enough in this context. The most glamorous part of the charging system is the alternator. It is located directly under the front engine cover and is driven by the crankshaft. It converts mechanical energy provided by the engine into electrical energy.
Electrical current is provided to the field by the brushes and slip rings.
The slip rings are the two copper rings that are located just behind the front bearing. They rotate with the rotor and crankshaft. The brushes are the squared-off carbon rods which are pushed up against the slip rings by two springs, one per brush. The brushes are stationary and as they rub across the slip rings they maintain contact and allow current to be transferred from the stationary part of the alternator to the rotating part. The outer part of the alternator is called the stator, once again a fairly obvious name as it remains stationary.