The voltage regulator, flasher units, and fuse box are the control and protection components of the electrical system. Each changed during production, and the correct specification depends on both the production date and whether the car is dynamo or alternator-equipped.
Dynamo Control Box
The dynamo control box (voltage regulator) is fitted to dynamo-equipped cars only and controls the charging output by regulating the field current to the dynamo. Two control box types were used: the RB106 for dynamo-equipped cars and the RB340 for alternator-equipped cars, the alternator version serves as a junction box rather than a true regulator, as the alternator has its own internal regulation. The control box must be matched to the car's charging system. A faulty regulator typically manifests as either no charging (ignition warning light stays on while driving) or overcharging (boiling battery, blown bulbs).
Instrument Voltage Stabiliser
The instrument voltage stabiliser provides a constant 10-volt supply to the fuel and temperature gauges regardless of the car's system voltage fluctuations. A faulty stabiliser causes gauge readings that fluctuate with engine speed, the fuel gauge needle bouncing in time with the revs is the classic symptom.
Replacement stabilisers are available in both the original bi-metallic type (which pulses the voltage on and off to achieve an average of 10 volts, causing a slight needle oscillation that is normal) and a modern solid-state electronic version that provides smoother, more consistent regulation.
Flasher Units
Three flasher unit types were used across production: a three-terminal unit, a two-terminal unit, and a hazard flasher unit (on cars with hazard warning lights fitted). The correct type depends on the car's production date and indicator circuit wiring. LED-compatible electronic flasher units are available for cars fitted with LED indicator bulbs, the standard bi-metallic flasher interprets the reduced current draw of LEDs as a blown bulb and doubles the flash speed.
Fuse Box
Two fuse box types were used: an early two-fuse type and a later four-fuse type, reflecting the increasing complexity of the electrical system across production. Fuse box covers and replacement glass fuses are available for both types. A fuse box cover label showing the correct fuse ratings for the specific car should always be fitted, a blown fuse replaced with an incorrect higher rating can allow a circuit to carry excessive current without blowing, risking wire damage or fire. The fuse box connections and earth points should be cleaned periodically, as corroded fuse terminals are a common cause of intermittent electrical faults.
Solenoids
The starter solenoid and the starter push-button solenoid are available for all production periods. The rubber cap covering the solenoid terminals should be renewed if perished, as an exposed solenoid terminal in the engine bay is a potential short-circuit hazard if a stray wire or tool contacts it.