Section 17-01: Lighting, Exterior
1994 Mustang Workshop Manual
DIAGNOSIS AND TESTING

Pinpoint Tests—Headlamps

 

PINPOINT TEST AA: HEADLAMPS INOPERATIVE

 

AA1 CHECK SUPPLY VOLTAGE AT HEADLAMP SWITCH 

Yes
GO to AA4.

No
GO to AA2.

 

AA2 CHECK HEADLAMP FUSE

Yes
SERVICE Circuit 38 (BK/O) for an open circuit. RESTORE vehicle. RETEST system.

No
GO to AA3.

 

AA3 CHECK CIRCUIT 38 (BK/O)

  • Remove headlamp fuse (50A).
  • Using a test lamp connected to battery (+), connect other end to the output side of fuse cavity.
  • Did test lamp illuminate?
Yes
SERVICE Circuit 38 (BK/O) for a short to ground. RESTORE vehicle. RETEST system.

No
REPLACE damaged headlamp fuse (50A). RESTORE vehicle. RETEST system.

 

AA4 CHECK HEADLAMPS SWITCH OUTPUT

  • Actuate the headlamp switch to the HEAD position.
  • Using a test lamp connected to a known good ground, check Pin H at headlamp switch for voltage.
  • Did test lamp illuminate?
Yes
GO to AA5.

No
REPLACE damaged headlamp switch . RESTORE vehicle. RETEST system.

 

AA5 CHECK HEADLAMP INPUT TO TURN SIGNAL AND WINDSHIELD WIPER SWITCH

  • Headlamp switch still in the HEAD position.
  • Gain access to the turn signal and windshield wiper switch connector.
  • Using a test lamp connected to a known good ground, check Pin 2 Circuit 15 (R/Y) at turn signal and windshield wiper switch .
  • Did test lamp illuminate?
Yes
GO to AA6.

No
SERVICE Circuit 15 (R/Y) for an open circuit. RESTORE vehicle. RETEST system.

 

AA6 CHECK TURN SIGNAL AND WINDSHIELD WIPER SWITCH

  • Test lamp still connected to ground, check Pin 3 Circuit 13 (R/BK) at turn signal and windshield wiper switch connector.
  • Did test lamp illuminate?
Yes
GO to AA7.

No
REPLACE damaged turn signal and windshield wiper switch . RESTORE vehicle. RETEST system.

 

AA7 CHECK CIRCUIT 14 (BR) AT HEADLAMP SWITCH

  • Headlamp switch still in the HEAD position.
  • Using a test lamp connected to a known good ground, check Circuit 14 (BR) at headlamp switch Pin R for voltage.
  • Did test lamp illuminate?
Yes
SERVICE Circuit 14 (BR) for an open circuit. RESTORE vehicle. RETEST system.

No
GO to AA8.

 

AA8 CHECK SUPPLY TO PARKING LAMPS

  • With test lamp still connected to ground, check Circuit 195 (T/W) Pin B2 at headlamp switch .
  • Did test lamp illuminate?
Yes
REPLACE damaged headlamp switch . RESTORE vehicle. RETEST system.

No
GO to AA9.

 

AA9 CHECK SUPPLY CIRCUIT TO HEADLAMP SWITCH

  • Using a test lamp connected to a known good ground, check Circuit 195 (T/W) at output side of fuse 5 (15A)
  • Did test lamp illuminate?
Yes
SERVICE Circuit 195 (T/W) for open circuit. RESTORE vehicle. RETEST system.

No
GO to AA10.

 

AA10 CHECK CIRCUIT 195 (T/W) FOR SHORT

  • Using an ohmmeter connected to ground, connect second lead to output side of Fuse 5 (15A) cavity. Measure resistance.
  • Is resistance 5 ohms or less?
Yes
SERVICE Circuit 195 (T/W) for short to ground. RESTORE vehicle. RETEST system.

No
REPLACE damaged Fuse 5 (15A). RESTORE vehicle. RETEST system.

 

AA11 CHECK SUPPLY TO SUSPECT HEADLAMP 

  • Actuate headlamp switch to the HEAD position.
  • Gain access to the suspect headlamp connector. Disconnect the suspect headlamp .
  • Using a test lamp connected to a known good ground, connect other end to Circuit 13 (R/BK) at headlamp connector.
  • Did test lamp illuminate?
Yes
GO to AA12.

No
SERVICE Circuit 13 (R/BK) for open circuit. RESTORE vehicle. RETEST system.

 

AA12 CHECK SUSPECT HEADLAMP GROUND

  • Using an ohmmeter connected to a known good ground, connect second lead to Circuit 57 (BK) at headlamp connector. Measure resistance.
  • Is resistance 5 ohms or less?
Yes
REPLACE damaged headlamp miniature bulb . RESTORE vehicle. RETEST system.

No
SERVICE Circuit 57 (BK) for open circuit. RESTORE vehicle. RETEST system.

 

AA13 CHECK SUPPLY VOLTAGE TO SUSPECT REAR LAMP 

  • Actuate headlamp switch to the parking lamp position.
  • Gain access to suspect rear lamp connector. Disconnect the suspect rear lamp .
  • Using a test lamp connected to a known good ground, connect the other end to Circuit 14 (BR) at rear lamp connector.
  • Did test lamp illuminate?
Yes
GO to AA14.

No
SERVICE Circuit 14 (BR) for open circuit. RESTORE vehicle. RETEST system.

 

AA14 CHECK SUSPECT REAR LAMP GROUND

  • Using an ohmmeter connected to a known good ground, connect second lead to Circuit 57 (BK) at rear lamp connector. Measure resistance.
  • Is resistance 5 ohms or less?
Yes
REPLACE damaged rear lamp miniature bulb . RESTORE vehicle. RETEST system.

No
SERVICE Circuit 57 (BK) for open circuit. RESTORE vehicle. RETEST system.

 

AA15 CHECK CIRCUIT 14 (BR) AT HEADLAMP SWITCH 

  • Actuate headlamp switch to the park position.
  • Using a test lamp connected to a known good ground, check Circuit 14 (BR) at headlamp switch Pin R for voltage.
  • Did test lamp illuminate?
Yes
SERVICE Circuit 14 (BR) for an open circuit. RESTORE vehicle. RETEST system.

No
GO to AA16.

 

AA16 CHECK SUPPLY TO PARKING LAMPS

  • With test lamp still connected to ground, check Circuit 195 (T/W) Pin A at headlamp switch .
  • Did test lamp illuminate?
Yes
REPLACE damaged headlamp switch . RESTORE vehicle. RETEST system.

No
GO to AA17.

 

AA17 CHECK SUPPLY CIRCUIT TO HEADLAMP SWITCH

  • Using a test lamp connected to a known good ground, check Circuit 195 (T/W) at output side of fuse 5 (15A).
  • Did test lamp illuminate?
Yes
SERVICE Circuit 195 (T/W) for open circuit. RESTORE vehicle. RETEST system.

No
GO to AA18.

 

AA18 CHECK CIRCUIT 195 (T/W) FOR SHORT

  • Using an ohmmeter connected to ground, connect second lead to output side of fuse 5 (15A) cavity. Measure resistance.
  • Is resistance 5 ohms or less?
Yes
SERVICE Circuit 195 (T/W) for short to ground. RESTORE vehicle. RETEST system.

No
REPLACE damaged fuse 5 (15A). RESTORE vehicle. RETEST system.