AUTOMOTIVE ELECTRICAL CIRCUITS AND WIRING

A common problem arises when a CARBON TRACE (small line of carbonlike
substance that conducts electricity) forms on the inside of the distributor cap or outer
edge of the rotor. The carbon trace will short coil voltage to ground or to a wrong
terminal lug in the distributor cap. A carbon trace will cause the spark plugs to either
fire poorly or not at all.
Using a droplight, check the inside of the distributor cap for cracks and carbon trace.
Carbon trace is black which makes it hard to see on a black-colored distributor cap. If
carbon trace or a crack is found, replace the distributor cap or rotor.
CONTACT POINT DISTRIBUTOR SERVICE.- In a contact point distributor,
there are two areas of concern- the contact points and the condenser.
Bad contact points cause a variety of engine performance problems. These problems
include high-speed missing, no-start problem, and many other ignition troubles.
Visually inspect the surfaces of the contact points to determine their condition. Points
with burned and pitted contacts or with a worn rubbing block must be replaced.
However, if the points look good, point resistance should be measured. Turn the
engine over until the points are closed and then use an ohmmeter to connect the meter
to the primary point lead and to ground. If resistance reading is too high, the points are
burned and must be replaced.
A faulty condenser may leak (allow some dc current to flow to ground), be shorted
(direct electrical connection to ground), or be opened (broken lead wire to the
condenser foils). If the condenser is leaking or open, it will cause point arcing and
burning. If the condenser is shorted, primary current will flow to ground and the
engine will NOT start. To test a condenser using an ohmmeter, connect the meter to
the condenser and to ground. The meter should register slightly and then return to
infinity (maximum resistance). Any continuous reading other than infinity indicates
that the condenser is leaking and must be replaced.
Installing contact points is a relatively simple procedure but must be done with
precision and care in order to achieve good engine performance and economy. Make
sure the points are clean and free of any foreign material.
Proper alignment of the contact points is extremely important (fig. 2-52). If the faces
of the contact points do not touch each other fully, heat generated by the primary
current cannot be dissipated and rapid burning takes place. The contacts are aligned by
bending the stationary contact bracket only. NEVER BEND THE MOVABLE
CONTACT ARM. Ensure the contact arm-rubbing block rests flush against the
distributor cam. A small amount of an approved lubricate should be placed on the
distributor cam to reduce friction between the cam and rubbing block. Once the points
are installed, they can be adjusted using either a feeler gauge or dwell meter.
To use a feeler gauge to set the contact points, turn the engine over until the points are
FULLY OPEN. The rubbing block should be on top of a distributor cam lobe. With
the points open, slide the specified thickness feeler gauge between them. Adjust the
points so that there is a slight drag on the blade of the feeler gauge. Depending upon
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