Every MGA was built with the Lucas 12-volt electrical system with positive earth, an architectural point that applies to all variants (1500, 1600, 1600 Mk II, Twin Cam, De Luxe) and affects every component in this category. Positive earth means the positive battery terminal is connected to the chassis and the negative terminal supplies current to the ancillaries, opposite to the negative earth convention used on later BMC cars and universal on modern vehicles. This matters for parts ordering throughout the electrical system: dynamos, coils, fuel pumps, radios and accessories must be polarised correctly for the system, and negative-earth components fitted to a positive-earth MGA without conversion will not work properly or may be damaged. The MGA's electrical system uses two 6-volt batteries connected in series to give the 12-volt supply, mounted in cradles on the chassis frame behind the seats and accessed by lifting the floor of the hood stowage compartment.
This section covers the complete electrical system across twelve sub-categories: batteries and cables, battery chargers and conditioners, dynamo and alternator, regulators/relays/fuse boxes, gauges, coil and HT leads, distributor, lighting, starter motor, switches and horns, wiring looms, and electrical upgrades and alternatives.
Charging system, dynamo (factory), alternator (upgrade)
All MGAs were supplied from factory with a Lucas dynamo, a C39PV-2 on 1500 and Twin Cam, or a C40-1 / C40 on 1600 from engine number 16GA/6272. A 1500 production-change affects visual identification: the windowless yoke dynamo (without brush gear inspection windows) was introduced at engine number 15GB/487. Twin Cam dynamos were the C39PV-2 design modified for the twin-cam engine. All factory dynamos were originally painted red to match the engine; some replacements are black.
Negative-earth alternator conversions are a common modern upgrade, covered under the Upgrades & Alternatives node.
Starter motor
The factory starter motor is the Lucas M35G-1 on all variants. The internals were redesigned on the 1600 Mk II from engine number 16GC/6435 (listed as the M35 type, interchangeable with the original). The starter position was raised at car/chassis 61504 with the introduction of the 15GD engine on late 1500 cars; the starter motor itself was not changed, but a rubber cover was added between the gearbox tunnel and the right-hand toeboard to protect the exposed Bendix spring, also found on Twin Cam and all 1600 models.
Control box and fuse box
The control box (dynamo voltage regulator) is the Lucas RB106-2 on most cars including the Twin Cam, modified on the 1600 from engine number 16GA/6272 when Lucar snap connectors were introduced on the dynamo harness, probably coinciding with the main harness change at car/chassis 74489. From approximately January 1961, the carbon composite resistance inside the control box was replaced with an improved wire-wound type. The control box is mounted on the left-hand side of the bulkhead on RHD cars and on the right-hand side on LHD cars. All MGAs use a single fuse box, the Lucas SF6, with two 35-amp fuses in circuit and two spares, a minimal fusing arrangement by modern standards.
Lighting, market-specific
MGA lighting is heavily market-specific, with distinct headlamp, sidelamp and rear lamp specifications for home-market RHD cars, European LHD cars, and North American cars. Most MGAs had Lucas F700 Mark VI headlamps; the P700 tripod lamps often seen today were never original fitment. Sidelamp specification changed from type 539 to the larger type 632 at Twin Cam chassis 2193 and from the start of 1600 production. Rear lamps: type 549 on the 1500, Twin Cam and 1600 Mk I; the entirely new type 647 (similar to Austin/Morris Mini Mk I) on the 1600 Mk II, mounted on horizontal plinths on the rear panel.
Full detail is under the Lighting node.
Wiring harness
Harness construction changed during production. Early 1500 cars (until approximately 1958) used cloth-covered individual wires with a black outer braid having a six-ply white cross pattern.
Later cars used PVC-insulated wires with plastic covering; harness braiding carries a yellow tracer on pushrod cars and a white tracer on Twin Cams. Some late Mk II cars had a grey rather than black harness cover. Full loom detail is under the Wiring Looms node.
Ordering considerations
Electrical parts selection starts with the variant, the chassis number, the drive hand (RHD or LHD, affecting control box location, dipswitch, and some lighting), and the export market the car was originally supplied to (which determines headlamp dip pattern, lens colours, rear lamp specification, and number plate lamp type).