Ford 2003 Mustang Workshop Manual page 3411

Is the voltage greater than 10 volts?
H11 CHECK FOR GROUND TO THE SUBWOOFER AMPLIFIER
HARNESS
NOTE: Ground circuit 694 is located in the same cavity in all four
subwoofer amplifiers.
Measure the resistance between subwoofer amplifier pins 2, circuit
694 (BK/LG) and ground.
Is the resistance less than 5 ohms?
H12 CHECK FOR AN AUDIO SIGNAL TO THE AFFECTED
SUBWOOFER AMPLIFIER
Key in ON position.
NOTE: Audio signal circuits 169 and 172 are located in the same
cavity on all four subwoofers.
Turn on the audio unit and check for a fluctuating AC voltage
between affected subwoofer amplifier pin 8, circuit 172 (LB/RD) and
pin 7, circuit 169 (LG/BK).
Does the voltage vary as the volume is adjusted?
H13 CHECK AUDIO SIGNAL CIRCUITS AT THE AFFECTED
SUBWOOFER AMPLIFIER FOR OPEN AND SHORT TO GROUND
Key in OFF position.
Disconnect: Audio Unit C290a.
Measure the resistance between the affected subwoofer amplifier
and the audio unit C290a, and between the affected subwoofer
amplifier and ground as follows:
operation.
Yes
GO to H12 .
No
REPAIR the circuit
(s) in question.
TEST the system
for normal
operation.
Yes
GO to H14 .
No
GO to H13 .
Yes
SEND the audio
unit to an
authorized Ford
audio system