Ford 2003 Mustang Workshop Manual page 2042

Measure the voltage between the central junction box fuse 6,
circuit 33 (WH/PK) and ground while holding the key in the
START position.
Is the voltage greater than 10 volts?
B8 CHECK CIRCUIT 1050 (LG/VT) FOR VOLTAGE
Key in OFF position.
Disconnect: Ignition Switch C209.
Key in ON position.
Measure the voltage between the ignition switch connector
C209 pin B4, circuit 1050 (LG/VT) and ground.
Is the voltage greater than 10 volts?
B9 CHECK THE IGNITION SWITCH
Carry out the ignition switch component test. Refer to
Refer to Wiring Diagrams Cell
information.
.
Does the ignition switch test good?
B10 CHECK CIRCUIT 1205 (BK) FOR OPEN
Key in OFF position.
149 for schematic and connector
system for normal
operation.
No
GO to B8 .
Yes
GO to B9 .
No
REPAIR circuit 1050
(LG/VT). TEST the
system for normal
operation.
Yes
REPAIR circuit 33
(WH/PK). TEST the
system for normal
operation.
No
INSTALL a new ignition
switch. TEST the
system for normal
operation.
Yes
INSTALL a new starter
motor relay. TEST the
system for normal
operation.
No
REPAIR circuit 1205
(BK). TEST the system
for normal operation.