A control module and magnetic pickup are mounted in the distributor, in place of a conventional ignition system's breaker points and condenser.
A wider spacing was also needed between the cap, inserts and the distributor housing to prevent arc-over and leakage to ground.
To prevent ignition failure due to carbon tracking, a special material is used for the distributor cap and rotor.
The spark plug wires are a carbon-impregnated cord conductor encased in an 8 millimeter diameter silicone jacket.
[citation needed] The five-pin module was introduced in 1978 and was an early attempt at electronic timing control; it contains a provision for connecting a knock sensor.
[citation needed] The seven- and eight-pin modules are used on early computer-controlled engines in conjunction with fixed-timing distributors, as the computer controls the ignition timing.
Increased secondary inductance provide a higher voltage and a longer spark duration than the conventional system.
HEI distributors are a popular swap on older GM cars originally equipped with points and condenser type ignition systems.