The MGB GT V8 electrical system uses a 12-volt negative-earth layout with a V8-specific wiring loom (loom number VL601 for chrome-bumper cars, VL602 for rubber-bumper cars). The system was unique to the V8 from manufacture, with revised loom routings to suit the V8 engine bay layout, V8-specific ignition components, and V8-specific switching for items such as the overdrive engagement on the column stalk. The 4-fuse fusebox (part number 37H4727) protects the major circuits with 35-amp and 50-amp fuses; many circuits are unfused on the original specification.
Charging System
The factory charging system uses an AC Delco alternator (part number 7982707) driven by a belt from the engine crankshaft pulley, providing high-output charging for the battery and electrical loads. The alternator is V8-specific in mounting and wiring; the four-cylinder MGB used Lucas alternators of different specification. Charging system warning is via a dashboard ignition warning light.
Starter Motor
The factory V8 starter motor is the Lucas 3M100, a powerful pre-engaged starter mounted on the V8 bellhousing. Engagement is controlled via a starter relay, the rectangular relay (part number 142169) was used up to 1976; a round relay (CHM68) was fitted to 1976 cars only. The starter relay receives switching signal from the ignition switch and routes battery power to the starter motor.
Distributor and Ignition
The factory V8 distributor is a Lucas item with vacuum and centrifugal advance, driven from the engine camshaft. Points-and-condenser specification was original; modern electronic ignition conversions are a popular upgrade. The ignition coil and ignition components feed the distributor and provide the spark for each cylinder in the firing order.
Wiring Loom
The V8 wiring loom is unique, VL601 for chrome-bumper specification, VL602 for rubber-bumper specification. The loom routes from the bulkhead-mounted fusebox to all electrical components on the car, with engine-bay sections, dashboard sections, lighting circuits and rear-end loops connecting at multi-pin connector blocks. The V8 loom is not interchangeable with any four-cylinder MGB loom.
Battery and Cables
Battery layout is V8-specific in some details, the battery uses a V8-unique terminal post (part number BHA5241), with positive cables BHH1256 (chrome-bumper) and BHH1257 (rubber-bumper). The battery is mounted in the boot floor area (chrome-bumper) or in the same general location with revised mounting (rubber-bumper).
Sub-Sections
Wash/Wipe, Batteries and Cables, Alternator, Starter Motor, Distributor, Ignition Components, Regulators Relays and Fuse Boxes, Lighting, Gauges and Cables, Horns and Fixings, Switches, Wiring Looms each cover their respective subsystems. Upgrades and Alternatives covers performance ignition, electronic distributors, high-output alternators, hi-torque starters and lighting upgrades.
MGOC Spares
MGOC Spares supplies the full range of MGB GT V8 electrical components, see individual sub-sections for details.