Cadillac 60 Series 1963 Shop Manual page 299

12-18
ELECTRICAL SYSTEM
Voltmeter
Black
Good Engine Ground
Brown Lead To Windshield
^ ^ Wiper Motor
To Starting
Motor
Fig. 12-23 Ignition Primary Circuit Resistance Test
c. Unusually high readings at two or more plugs
indicate a cracked distributor cap or insulation
breakdown between spark plug cables.
d. Low reading at all plugs indicates excessive
resistance in either the primary or secondary
circuit, or a weak coil.
e. If the reading is unusually low at one or two
plugs, it indicates a ground at the distributor cap,
the spark plug cable or the plug itself.
Remove the plug cable and black lead from the
plug and note the reading. If the reading improves,
the spark plug is grounded or shorted. If the read-
ing does not improve, check plug cable and distrib-
utor cap.
25. Ignition Primary Circuit
Resistance Test
Excessive voltage drop in the primary circuit
will lessen the secondary output of the ignition
coil, resulting in h a r d starting and poor
performance.
1. Turn the voltmeter selector switch of the
Volt-Ampere Tester to the .4 volt position.
2. Connect test leads as shown in Fig. 12-23.
3. Remove coil secondary wire from distributor
and ground.
4. Close breaker points by rotating engine a
fraction of a revolution at a time with starting
motor.
5. Be sure all lights and accessories are turned
off.
6. Turn ignition switch "On". Voltmeter should
read not more than .4 volt.
7. Test ignition switch by turning it off and on
several times. Voltmeter should record the same
reading each time switch is turned on.
NOTE: While switch is being turned on and
off, key should be jiggled in switch several
times and voltmeter checked for any change in
readings.
8. Test all wires for tightness. Move them about
and not note any change in meter reading.
9. Remove voltmeter leads and place them across
the primary wires from coil to distributor as
shown by dotted leads in Fig. 12-23. Voltmeter
should read less than .1 volt.
NOTE: If voltmeter reading exceeds the
specified maximum, isolate the point of this
resistance by placing the test leads across each
connection and wire in order. The reading
across a connection should be proportionate to
its length as compared to the length and allow-
able voltage drop of the entire circuit.
26. Ignition Coil Test
The coil in the ignition circuit of an engine acts
as a transformer by stepping up battery voltage
to a voltage sufficiently high to jump the rotor
gap in the distributor and the spark plug gap
while the cylinder is under compression. The
common causes of coil failure are:
1. High resistance due to corroded connections
or broken wires.
2. Short circuits or breakdown of insulation be-
tween turns of the coils and grounds.
3. Breakdown of insulation between the wind-
ings and the core or case,
a. Reading Coil Tester Meter
The OHM scale on the coil test unit is to be
used for measuring the resistance form 0 ohms
to 100,000 ohms.
To calibrate the unit, connect the positive pri-
mary and the ground lead clips together. Turn
the switch to the "Dwell-Ohm" position.
Adjust the "Dwell-Ohm" Regulator until the
meter reads on the set line. Disconnect the leads.
Connect the unit in which resistance is being
measured in series with the test leads. The meter
will then indicate the amount of resistance in the
unit.
The "Ohm" scale is read from right to left
from 0 to 100,000 ohms. From 0 to the first
graduation indicates 100 ohms, 50 indicates 500
ohms, 1M indicates 1,000 ohms, 100M indicates
100,000 ohms.