Ignition Cable: Description and Operation

PURPOSE
The secondary ignition wires conduct ignition voltage from the ignition coil to the distributor and spark plugs.

CONSTRUCTION
The secondary ignition wires (spark plug wires and ignition coil wire) are "suppressor" wires and consist of a carbon impregnated conductor cord encased in an 8mm silicone rubber jacket insulator. The carbon conductor core provides moderate resistance (approx. 10K ohms/foot) to help reduce radio static interference. The silicone jacket withstands very high temperature and also provides an excellent insulator for the higher voltage of the electronic ignition system. At each end of the wires is an insulator "boot" also made of high silicone rubber. The boots form a tight seal on the plugs and distributor cap. Boots cover the terminals on the distributor and extend over a portion of the spark plug insulators to prevent ignition voltage from arcing to other grounds.

OTHER NOTES
A "corona" may be visible as a steady blue light appearing around the spark plug boot or porcelain insulator, just above the shell crimp. This is the slight visible effect produced by the electric/magnetic field created by high voltages, and has no effect on ignition performance. The corona is not usually visible except in darkness. This discharge may repel dust particles, leaving a clear ring on the insulator just above the shell. This ring is sometimes mistakenly regarded as evidence that combustion gases have blown out between the shell and the insulator.

DO NOT mistake corona discharge for flash-over or a shorted insulator. If arcing through the insulation is suspected, attach a long piece of wire to a screwdriver (or other tool with an insulated plastic handle) and to a ground on the engine. With the engine running, hold the tip of the screwdriver near the location where arcing is suspected, or run it along the length of the plug wires. If the spark plug is cracked, or the wire insulation or boot has failed, you should see a bright blue spark jump to the screwdriver when passing near the bad spot. If no spark is observed, wire insulation and boot are OK.