We'll start with the distributor shaft, which is either driven directly by the camshaft or at a ratio of 2:1 by the crankshaft. This goes into the distributor, which has a lower part made of metal and and a plastic distributor cap held mostly either by springs or screws. Right at the bottom, just after the shaft enters into the the round casing, is the centrifugal-force adjustment for adapting the ignition to the engine speed.
In the casing, above the centrifugal-force adjustment, there is a rotatable plate, onto which mostly only one interrupter contact is mounted. It is operated by the same amount of cams on the distributor shaft as the engine has cylinders. In the case of very many cylinders, this
function can be shared by two distributors. The load-dependent plate is turned against the spring force by a single or double vacuum unit.
To avoid sparking on the contact points a parallel connected condenser is present. Thus, the ignition control is accomodated on the primary side. Although the control on the secondary side is only one floor higher, the control cable-1 first leads to the asphalt ignition coil, which only in the beginning of 1980, was replaced by different construction types.
Coming back from there, is a highly insulated ignition cable, also called terminal-4. It is connected to the center contact of the distributor cap, also called the center dome. In this is a piece of sprung carbon, which connects the cable electrically to the rotating distributor finger when the engine is running. Although it is only slipped over the distributor shaft, it only snaps into place in one certain position.
From the center of the distributor finger, the current goes through an in-cast interference suppression out to it's point, it then passes the current to the individual ignition cables through the contacts, without actually touching them and strictly following the firing order. Here the spark simply jumps over to the nearest contact point. Thus, both the cams below and the distributor finger are in very definite positions.
Through the ignition cables (plug-leads) we come to the individual spark plugs. They have only one visible connection, the spark plug cap. The electric circuit is closed through the metal of the engine. The individual plug-leads must also be placed exactly in the firing order. Leads on the wrong spark plugs will be rewarded with loud misfiring and the engine won't start. 05/12