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

Pinpoint Tests—Stoplamps

 

PINPOINT TEST BA: STOPLAMPS/HIGH-MOUNT STOPLAMPS INOPERATIVE

 

BA1 CHECK SUPPLY TO STOPLIGHTS 

Yes
GO to BA4.

No
GO to BA2.

 

BA2 CHECK SUPPLY CIRCUIT TO STOPLIGHT SWITCH

Yes
SERVICE Circuit 10 (LG/R) for open circuit. RESTORE vehicle. RETEST system.

No
GO to BA3.

 

BA3 CHECK CIRCUIT 10 (LG/R) FOR SHORT

  • Using an ohmmeter connected to ground, connect second lead to output side of fuse 9 (15A) cavity. Measure resistance.
  • Is resistance 5 ohms or less?
Yes
SERVICE Circuit 10 (LG/R) for short to ground. RESTORE vehicle. RETEST system.

No
REPLACE damaged fuse 9 (15A). RESTORE vehicle. RETEST system.

 

BA4 CHECK STOPLIGHT SWITCH OUTPUT

  • Apply brake pedal and hold.
  • Using a test lamp connected to a known good ground, check Circuit 810 (R/LG) at stoplight switch .
  • Did test lamp illuminate?
Yes
GO to BA5.

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

 

BA5 CHECK STOPLIGHT INPUT TO TURN SIGNAL AND WINDSHIELD WIPER SWITCH

  • Gain access to the turn signal and windshield wiper switch . With a test lamp connected to a known good ground, connect other end to Circuit 810 (R/LG) at Pin G of turn signal and windshield wiper switch connector.
  • Apply brake pedal and hold.
  • Did test lamp illuminate?
Yes
GO to BA6.

No
SERVICE Circuit 810 (R/LG) for open circuit. RESTORE vehicle. RETEST system.

 

BA6 CHECK TURN SIGNAL AND WINDSHIELD WIPER SWITCH OUTPUT TO STOP LAMPS

  • Using a test lamp connected to a known good ground, and brake pedal still applied, check Circuit 9 (LG/O) at Pin C of turn signal and windshield wiper switch connector, or Circuit 5 (O/LB) Pin D of turn signal and windshield wiper switch connector.
  • Did test lamp illuminate?
Yes
LEAVE brake pedal applied. GO toBA7.

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

 

BA7 CHECK STOPLIGHT SUPPLY TO MINIATURE BULB

  • Gain access to either stoplight connector. Disconnect stoplight connector.
  • Using a test lamp connected to a known good ground, check either Circuit 9 (LG/O) or Circuit 5 (O/LB) for voltage.
  • Did test lamp illuminate?
Yes
GO to BA8.

No
SERVICE Circuit 9 (LG/O) or Circuit 5 (O/LB) for open circuit. RESTORE vehicle. RETEST system.

 

BA8 CHECK STOPLIGHT GROUND

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

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

 

BA9 CHECK SUPPLY TO HI-MOUNT STOPLIGHT 

  • Remove rear hi-mount lamp as outlined.
  • Connect one end of a test lamp to a known good ground, connect other end to Circuit 810 (R/LG) at stoplight connector.
  • Apply brake pedal .
  • Did test lamp illuminate?
Yes
RELEASE brake pedal. GO to BA10.

No
SERVICE Circuit 810 (R/LG) for open circuit. RESTORE vehicle. RETEST system.

 

BA10 CHECK REAR HI-MOUNT LAMP GROUND

  • Connect an ohmmeter to a known good ground. Connect second lead to Circuit 57 (BK) at stoplight connector. Measure resistance.
  • Is resistance 5 ohms or less?
Yes
REPLACE damaged stoplight miniature bulb . REPLACE LED lamp assembly (Cobra). RESTORE vehicle. RETEST system.

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