Pontiac FIREBIRD 1972 Service Manual page 1273

CHASSIS ELECTRICAL 12-3
LIGHTING AND HORN POWER CIRCUITS
blown fuses. In each, trouble diagnosis requires following
through the circuits until the source of difficulty is found.
Troubles in the lighting and horn power circuits are
TO aid in making an orderly check, refer to the wiring
caused by loose connections, open or shorted wiring, or
diagrams shown in the end of Section 12.
HORNS WILL NOT OPERATE
NOTE: To locate trouble, connect jumper lead to number l and 3 termi-
nals of re& tenninal numbers are stamped on relay base. Ifhorn blows,
the trouble is in relay horn button or wiring. (To detennine whether relay
horn button or wining is at fault, ground No. 2 tenninal o f relay. I f horn
blows, horn button or winng is at fault.) I f horn does not blow and wiring
bet ween battery and relay is not defective, connect voltmeter bet ween horn
tenninal and horn mounting nut. Again connect jumper lead to number
I and 3 tenninals of relay and note voltmeter reading. I f no voltmeter
reading is obtained, wiring between relay and horn is open or horn is not
grounded. I f voltmeter reading is less than Z 0 volts, trouble is due to high
resistance connections in wiring or faulty horn. I f voltmeter reading is
above Z 0 volts, trouble is due to faulty horn.
CAUSE
Loose connections in circuit.
Defective horn switch.
Defective horn relay.
Defects within horn.
1.
Bench checks:
a. No current may indicate broken connection or open
circuit due to broken lead or overheating. Most horn
failures are caused by horns being operated continu-
ously. This develops sufficient heat to melt wires in
winding causing an open circuit. Overheating is ac-
companied by a characteristic odor which indicates
that horn should be replaced.
b. No current can also indicate contact points are open
and current adjustment is required. Turn adjusting
screw counterclockwise.
CORRECTION
Check and tighten connections. Be sure to check
ground straps.
Replace defective parts.
Replace relay.
Replace horn.
not opening. A current adjustment is required by
turning screw clockwise.
2.
Current adjustment for "Type-C" horns:
Current adjustment is made by turning adjusting screw
counterclockwise to increase current or clockwise to de-
crease current until specified current is reached. Care
must be taken not to turn adjusting screw too far. Turn
only 1/4 of turn at one time. If adjustment loosens screw
excessively, it may be staked with prick punch.
c. High current (over 20 amperes) indicates an over- The following adjustment of horn current should be made
heated winding or shorted horn which should be re-
using an automotive type battery and wires that are No.
placed. 16 gauge or larger:
.........................
d. A reading of approximately
18
amperes for
12
volt
Voltage Supply Adjust Horn Current To
....................................................
horn indicates condition in which contact points are 11.5-12.5~ .4.5-5.5 amps
HORNS HAVE POOR TONE
CAUSE
Low available voltage at horn.
Defects within horn.
CORRECTION
Check battery and charging circuit.
Although horn should blow at any voltage above
7.0 volts, a weak or poor tone may occur at
operating voltages below 11.0 volts. If horn has
weak or poor tone at operating voltage of
11.0
volts or higher, remove horn and replace.