Jeep 1987 Wrangler Workshop Manual page 1787

2.5L
4 . 2 L
IGNITION
HOT IN ACCY & RUN
F R O M I G N I T I O N S W I T C H
"T - — T FUSE
I GAUGES j PANEL
;i5amp
:™
ER
_ J DISTRIBUTION
TACHOMETER
DESCRIPTION
18 WHT
W/TR
1
BUZZER
MODULE
TACHOMETER
The tachometer is a solid state circuit requiring only
three connections for operation—battery feed, ground
and an engine speed input signal.
The solid state circuits in the tachometer are powered-up
through the ignition switch and the 15 amp gauges fuse. A
second wire connects the necessary circuits to ground.
The third wire connects the tachometer to the ignition
module which controls the ignition coil primary circuit.
The engine speed input signal is measured by the tach-
ometer solid state circuits and converted to needle move-
ment across the gauge face.
TROUBLESHOOTING —Tachometer
1. GAUGES FUSE: Turn ignition switch to RUN
T E S T O K NOT O K
Check operation of gauge
package
Gauge package operates
Check GAUGES fuse
Measure voltage at battery side
of GAUGES fuse
Battery voltage Repair open from ignition switch
2. IGNITION MODULE TACHOMETER OUTPUT SIGNAL: Connect AC
voltmeter to C130 terminal C-2.5L, C112 terminal A-4.2L; start engine
T E S T
OK
NOT O K
Operate engine at variable
speeds and note voltage readings
AC voltage varies with engine
speed
Replace ignition module
3. TACHOMETER INPUT SIGNAL' Connect AC voltmeter to C155 terminal
F; start engine
T E S T O K
NOT
O K
Operate engine at variable
speeds and note voltage readings
AC voltage varies with engine
speed
Repair open between ignition module and tachometer
SEE GROUND
DISTRIBUTION
Tachometer 19 Tachometer 19