Ford 2003 Mustang Workshop Manual page 3409

Is voltage indicated?
H5 CHECK THE AUDIO UNIT
Substitute a known good audio unit.
Verify the operation of the audio unit.
Does the audio unit operate correctly?
H6 CHECK THE VOLTAGE TO THE SUBWOOFER AMPLIFIER
Key in OFF position.
Disconnect: Subwoofer Amplifier C4109b.
Key in ON position.
Turn on the audio unit.
Measure the voltage between the subwoofer amplifier C4109b pin 5,
circuit 828 (VT/LB), harness side and ground; between the
subwoofer amplifier C4109b pin 6, circuit 828 (VT/LB), harness side
and ground; and between the subwoofer amplifier C4109b pin 7,
circuit 828 (VT/LB), harness side and ground.
Are the voltages greater than 10 volts?
H7 CHECK THE GROUND TO THE SUBWOOFER AMPLIFIER
Measure the resistance between the subwoofer amplifier C4109b pin
1, circuit 694 (BK/LG), harness side and ground; between the
Yes
SEND the audio
unit to an
authorized Ford
audio system
repair facility.
TEST the system
for normal
operation.
No
REMOVE the
subwoofer
amplifier and
SEND it to an
authorized Ford
audio system
repair facility.
TEST the system
for normal
operation.
Yes
GO to H7 .
No
REPAIR the circuit
(s) in question.
TEST the system
for normal
operation.
Yes
GO to H8 .