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

Pinpoint Test—Backup Lamps

 

PINPOINT TEST FA: BACKUP LAMPS INOPERATIVE

 

FA1 CHECK SUPPLY AT BACKUP LAMP SWITCH 

Yes
GO to FA4.

No
GO to FA2.

 

FA2 CHECK SUPPLY AT FUSE 1 (15A)

Yes
SERVICE Circuit 298 (P/O) for open circuit. RESTORE vehicle. RETEST system.

No
GO to FA3.

 

FA3 CHECK SUPPLY TO FUSE 1 (15A)

  • Using a test lamp, check input side of fuse 1 (15A).
  • Did test lamp illuminate?
Yes
REPLACE damaged fuse 1 (15A). RESTORE vehicle. RETEST system.

No
SERVICE Circuit 687 (GY/Y) for open circuit. RESTORE vehicle. RETEST system.

 

FA4 CHECK BACKUP LAMP SWITCH OUTPUT

  • Actuate shift control selector lever and housing to the reverse position.
  • Using a test lamp connected to ground check Circuit 140 (BK/PK) for voltage.
  • Did test lamp illuminate?
Yes
GO to FA5.

No
REPLACE damaged backup lamp switch (manual transmission) or manual lever position switch (automatic transmission). RESTORE vehicle. RETEST system.

 

FA5 CHECK SUPPLY TO BACKUP LAMPS

  • Gain access to backup lamps as outlined.
  • Disconnect backup lamp miniature bulb .
  • Using a test lamp connected to a known good ground, check Circuit 140 (BK/PK) for voltage.
  • Did test lamp illuminate?
Yes
GO to FA6.

No
SERVICE Circuit 140 (BK/PK) for open circuit. RESTORE vehicle. RETEST system.

 

FA6 CHECK BACKUP LAMP GROUND 

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

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