The MGB ignition system evolved across the production run, from the early positive earth cars with the Lucas 25D distributor through to the later negative earth cars with the 45D. Getting the ignition set up correctly has a disproportionate effect on how the MGB drives, a worn distributor, a faulty coil, or incorrectly set points will blunt throttle response, reduce fuel economy, and make cold starting unreliable regardless of the condition of the rest of the engine. The distributor type changed from the 25D with side-entry HT leads on early cars to a top-entry 25D from the MkII in late 1967, with the 45D fitted from 1974 on rubber bumper cars, a critical identification point when ordering caps, rotors, and points.
Replacement distributors, points, condensers, rotor arms, distributor caps, and vacuum advance units are available for both the 25D and 45D types. Ignition service kits supply the contact breaker points, condenser, rotor arm, and cap as a complete set. The ignition coil is available for both standard and sports applications. HT leads, spark plugs, plug caps, and all associated ignition wiring components are available.
Electronic ignition is available as a direct replacement for the contact breaker system, eliminating the wear and drift associated with mechanical points and providing a more consistent spark across the rev range. It is one of the most cost-effective single upgrades available for the MGB and is fully reversible, the original points can be refitted if required.