Lesson3/Learning Event 1
Engines used in the Army's tactical wheeled vehicles are designed to operate under water. This
means that the ignition system must be waterproof. The distributor is made waterproof by a cover
mounted over the distributor cap. The ignition coil is mounted inside the distributor housing and is
also protected from water by the cover. The cover contains threaded waterproof terminals for the
spark plug cables.
SECONDARY WIRING AND SPARK PLUGS
The secondary wiring is part of the high-voltage circuit outside the distributor. On civilian-type
vehicles, this wiring consists of a cable or wire from the ignition coil to the center tower in the
distributor cap. Other wires will lead from the outside towers to the spark plugs.
The wires themselves are very small, only a few strands of very fine wire. The insulation is very
thick to prevent the highvoltage current, traveling through the wire, from arcing to ground before it
gets to the spark plug.
Other type cables may use a carbon saturated string, instead of a wire, as a conductor. The main
reason for this is to cut down on noise that can be picked up by radio.
On waterproof ignition systems, the hightension cable will be inside of a waterproof tube. A woven
metal shielding around this tube will reduce radio interference (static) when the engine is running.
A nut and a waterproof seal are used on each end of the cable to make a waterproof connection at
the distributor and the spark plug.
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