Certain 1981–83 models used the EEC-III system, which uses a Dura-Spark III module (brown grommet where wires emerge) and a Dura-Spark II ignition coil. A resistance wire is used in the primary circuit. The distributors in EEC-III (and later) systems eliminate conventional mechanical and vacuum advance mechanisms. All timing is controlled by the engine computer, which is capable of firing the spark plug at any point within a 50-degree range depending on calibration. This increased spark capability requires greater separation of adjacent distributor cap electrodes to prevent cross-fire, another reason for its large-diameter distributor cap. This system is very similar to the systems used at MSD; MSD used the Duraspark during R&D.