Wiring diagram, multimeter and wiggling wires. If this comes through for you, it is directly from Ford's manual.
PINPOINT TEST A: THE CHARGING SYSTEM WARNING INDICATOR IS ON WITH THE ENGINE RUNNING
Test Step Result / Action to Take A1 CHECK THE BATTERY
Carry out the Battery — Condition Test to determine if the battery can hold a charge and is OK for use. REFER to Section 414-01. Is the battery OK?Yes GO to A2.
No INSTALL a new battery. REFER to Section 414-01. TEST the system for normal operation.
A2 CHECK FUSE 10 (10A) (All except PZEV), (1A) (PZEV) Check fuse: Fuse 10 (10A) (All except PZEV), (1A) PZEV) in the Battery Junction Box. Is the fuse 10 (10A) (All except PZEV), (1A) (PZEV) OK?Yes GO to A3.
No INSTALL a new fuse. TEST the system for normal operation. If the problem persists, check for a short to ground.
A3 CHECK THE CHARGING SYSTEM Carry out the Load Test using the diagnostic tool. Is the generator output OK?Yes DIAGNOSE the charging system warning indicator. REFER to Section 413-01.
No GO to A4.
A4 CHECK THE GROUND INTEGRITY Key in ON position. Measure the voltage between the generator housing and the negative battery terminal.
Is the voltage less than 0.5 volt?Yes GO to A5.
No CLEAN and TIGHTEN the generator mounting, engine-to-body ground strap, and battery ground cable. TEST the system for normal operation. If the concern persists, INSTALL a new battery ground cable. REFER to Section 414-01.
A5 CHECK BATTERY CABLE Key in ON position. Measure the voltage between the generator C102c B+ terminal circuit 30-BA6 (RD) and the positive battery terminal.
Is the voltage less than 0.5 volts?Yes GO to A6.
No CLEAN and TIGHTEN the positive battery cable connections. TEST the system for normal operation. If the concern persists, INSTALL a new positive battery cable. REFER to Section 414-01.
A6 CHECK BATTERY FEED TO THE GENERATOR Measure the voltage between the generator C102c B+ terminal, circuit 30-BA6 (RD), harness side and ground.
Is the voltage equal to the battery voltage?Yes GO to A7.
No REPAIR circuit 30-BA6 (RD) or circuit 30-BB10 (RD). TEST the system for normal operation.
A7 CHECK POWER TO THE VOLTAGE REGULATOR Key in OFF position. Disconnect: Generator C102a. Measure the voltage between the generator C102a pin 3, circuit 30-BA10 (RD), harness side and ground.
Is the voltage greater than 10 volts?Yes GO to A8.
No If fuse 10 (10A) (All except PZEV), (1A) (PZEV), is OK; REPAIR circuit 30-BA10 (RD). TEST the system for normal operation.
A8 CHECK POWERTRAIN CONTROL MODULE AND COMMUNICATIONS LINK WITH GENERATOR Connect: Generator C102a. Connect the diagnostic tool. Key in ON position. Retrieve PCM diagnostic trouble codes (DTCs). Are any DTCs retrieved?Yes Use the diagnostic tool to diagnose the PCM and communications.
No INSTALL a new generator. REFER to Section 414-02. TEST the system for normal operation.