The MGB GT V8 was fitted with a 4-fuse fusebox, part number 37H4727, protecting the major electrical circuits. The fusebox uses 35-amp and 50-amp glass cartridge fuses (different ratings on different fuses, depending on circuit current draw). Many circuits on the original factory specification are unfused, a reflection of 1970s electrical practice rather than modern safety standards. The fusebox is mounted in the engine bay area for accessibility, with circuit identification on the fusebox cover or in the workshop manual.
Fuses
Original specification fuses are glass cartridge type with end caps. Fuse blowing is always a fault diagnosis trigger, a blown fuse indicates an overload condition (short circuit, failed component drawing excessive current) that should be diagnosed and corrected before fitting a new fuse. Repeatedly blowing fuses with new units does not cure the underlying fault and can cause further damage.
Relays
Various relays are fitted around the car for circuits requiring switching of higher currents than the dashboard switches can handle directly, typically the headlamp circuits, the starter motor circuit (the starter relay covered separately under Starter Motor), and on some specifications the fuel pump and other heavy-current circuits. Relays comprise a small electromagnetic coil that operates a heavier set of contacts when energised.
Voltage Regulator
Where the alternator includes an external voltage regulator (some specifications integrate the regulator inside the alternator), the regulator controls alternator output to maintain correct system voltage. External regulators were common on dynamo systems and earlier alternator specifications; modern alternators typically have internal regulation. The factory V8 AC Delco alternator specification should be checked for regulator type.
Service Notes
Modern blade-fuse fuseboxes can be retro-fitted to replace the original 4-fuse glass cartridge fusebox, providing additional fused circuits and modern fuse types. The retrofit improves electrical system safety, particularly for cars where modern accessories have been added without proper fusing.
The original fusebox can be retained for originality where this is the priority.
MGOC Spares
MGOC Spares supplies V8 fuseboxes, fuses in original specifications, relays, voltage regulators and electrical protection components for the MGB GT V8.