Connects
To Switch		High Tension Wire
To Center Of Distributor		Connects To
Distributor
Primary
Winding		 Resistance
Unit
Secondary
Winding		 Iron Core
Condenser
Coil Bracket Must Be Grounded

Fig. 97. Delco Ignition Coil

The distributor and timer, together with the ignition coil, spark plugs, and wiring, constitute the ignition system.

The proper ignition of an internal combustion engine consists of igniting the mixture in each cylinder at such a time that it will be completely burned at the time the piston reaches dead center on the compression stroke. A definite period of time is required from the time the spark occurs at the spark plug until the mixture is completely expanded. It is therefore apparent, that, as the speed of the engine increases, the time the spark occurs must be advanced with respect to the crank shaft, and it is for this reason that the Delco ignition systems are fitted with an automatic spark control.

CIRCUIT BREAKER
AMMETER
COWL LIGHT
RESISTANCE UNITSWITCH
BRUSH SWITCHES
OPERATED BY
STARTING PEDAL		 CONDENSER
IGNITION COIL TONNEAU
LIGHT		HEAD
LIGHTS
SERIES FIELD ROTOR FOR DISTRIBUTING
HIGH TENSION CURRENT
MOTORGENERATOR TAIL LIGHT
STORAGE
BATTERY		 SHUNT
FIELD		TO SPARK PLUGS
DISTRIBUTOR		ADVANCE
TUNGSTEN
TIMING
CONTACTS		 AUX
LIGHT
HORN BUTTON
IN WHEEL

Fig. 98. Delco Wiring Diagram—Buick Cars

The quality of the mixture and the amount of compression are also factors in the time required for the burning to be complete. Thus a rich mixture burns quicker than a lean one. For this reason the engine will stand more advance with a half open throttle than with a wide open throttle, and in order to secure the proper timing of the ignition due to these variations and to retard the spark for starting, idling and carburetor adjusting, the Delco distributor also has a manual control.