Regulator rectifier

With the engine running, a healthy charging system on most models shows about 13.5–14.8 V across the battery terminals (see the manual for the exact value). The regulator turns surplus energy into heat, which is why its finned body gets hot.

Symptoms of a problem

• Not charging: the battery keeps going flat and voltage does not rise with revs
• Overcharging: voltage above 15 V; the battery swells or boils, bulbs blow frequently
• Burnt or melted connectors

Before replacing the regulator, also measure the stator output and check the wiring.