Ford 2003 Mustang Workshop Manual page 2039

Is the voltage greater than 12.5 volts?
A2 CHECK THE VOLTAGE TO THE STARTER MOTOR
SOLENOID
Measure the voltage between the starter motor solenoid
positive terminal and ground.
Is the voltage 12.5 volts or greater?
A3 MANUALLY JUMP THE STARTER MOTOR
Connect one end of a fused (15A) jumper wire to the
positive terminal of the battery and touch the other end to
the starter solenoid S-terminal.
Does the starter solenoid engage?
A4 TEST THE STARTER MOTOR RELAY
Carry out the relay component test on the starter motor
relay. Refer to the relay component test in this section.
Does the starter motor relay test good?
for an open. TEST the
system for normal operation.
Yes
GO to A3 .
No
REPAIR circuit 2037 (RD) for
an open. TEST the system
for normal operation.
Yes
GO to A4 .
No
INSTALL a new starter
motor. REFER to Starter
Motor—3.8L or Starter
Motor—4.6L . TEST the
system for normal operation.
Yes
REPAIR circuit 33
(WH/PK)/262 (BN/PK) for an
open. TEST the system for
normal operation.
No
INSTALL a new starter motor
relay. TEST the system for
normal operation.