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Home >> Mercury >> 2008 >> Milan Base, 3.0 1, FWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 1734 (Horn System) >> Diagnostic Tests >> Horn >> Pinpoint Tests >> Pinpoint Test A: The Horn Is Inoperative

Pinpoint Test A: The Horn Is Inoperative

WARNING: This page is about a different car, the 2010 Lincoln Town Car. However, it is still accessible from the selected car via links, so may be relevant.

Refer to SYSTEM WIRING DIAGRAMS , Horn/Cigar Lighter for schematic and connector information.

Normal Operation 

The horn relay control voltage and switched voltage circuit is supplied by the battery junction box (BJB) through circuit 1680 (OG/RD). The horn relay is controlled through circuit 1 (DB) by the horn switch. When the horn switch is pressed, the horn relay control circuit 1 (DB) is grounded through the clockspring and circuit 460 (YE/LB). The horn relay is then energized causing voltage to be applied to circuit 6 (YE/LG), enabling the horn to sound. Ground to the horn is supplied through circuit 57 (BK).

This pinpoint test is intended to diagnose the following:

PINPOINT TEST A: THE HORN IS INOPERATIVE 

NOTE: Use the correct probe adapter(s) when making measurements. Failure to use the correct probe adapter(s) may damage the connector.
NOTE: Failure to disconnect the battery when instructed will result in false resistance readings. Refer to GENERAL PROCEDURES .
  1. A1 CHECK CIRCUIT 1680 (OG/RD) FOR VOLTAGE 
    • Disconnect: Horn Relay
      • Fig 1: Checking Horn Relay Circuit Voltage
      GF0014483Courtesy of FORD MOTOR CO.
    • Measure the voltage between the horn relay pin 2, circuit 1680 (OG/RD), BJB face side and ground; and between the horn relay pin 3, circuit 1680 (OG/RD), BJB face side and ground.
    • Is the voltage greater than 10 volts? 
    1. YES  : Go to  A2.
    2. NO  : VERIFY the BJB fuse 10 (20A) is OK. If OK, REPAIR the circuit. TEST the system for normal operation.
  2. A2 CHECK THE HORN RELAY 
    • Substitute a known good relay.
    • Check the horn.
    • Dose the horn sound? 
    1. YES  : REMOVE the known good relay. INSTALL a new horn relay. TEST the system for normal operation.
    2. NO  : REMOVE the known good relay. Go to  A3.
  3. A3 CHECK THE HORN RELAY OUTPUT CIRCUITRY 
      Fig 2: Checking Horn Relay Output Circuit
      GF0014484Courtesy of FORD MOTOR CO.
    • Connect a fused (20A) jumper wire between the horn relay pin 3, circuit 1680 (OG/RD), BJB face side and the horn relay pin 5, circuit 6 (YE/LG), BJB face side.
    • Does the horn sound? 
    1. YES  : REMOVE the jumper wire. Go to  A6.
    2. NO  : REMOVE the jumper wire. Go to  A4.
  4. A4 CHECK CIRCUIT 6 (YE/LG) FOR AN OPEN 
    • Disconnect: Horn C131
      • Fig 3: Measuring Resistance
      GF0047680Courtesy of FORD MOTOR CO.
    • Measure the resistance between the horn relay pin 5, circuit 6 (YE/LG), BJB face side, and the horn C131-2, circuit 6 (YE/LG), harness side.
    • Is the resistance less than 5 ohms? 
    1. YES  : Go to  A5.
    2. NO  : REPAIR the circuit. TEST the system for normal operation.
  5. A5 CHECK THE HORN GROUND CIRCUIT 57 (BK) FOR AN OPEN 
      Fig 4: Checking Horn Ground Circuit
      GF0014486Courtesy of FORD MOTOR CO.
    • Measure the resistance between the horn C131-1, circuit 57 (BK), harness side and ground.
    • Is the resistance less than 5 ohms? 
    1. YES  : INSTALL a new horn. TEST the system for normal operation.
    2. NO  : REPAIR the circuit. TEST the system for normal operation.
  6. A6 CHECK CIRCUIT 1 (DB) BETWEEN THE HORN RELAY AND THE CLOCKSPRING FOR AN OPEN 
    • Depower the supplemental restraint system (SRS). Refer to GENERAL PROCEDURES article.
    • Disconnect: Clockspring C218a
      • Fig 5: Measuring Resistance
      GF0047681Courtesy of FORD MOTOR CO.
    • Measure the resistance between the horn relay pin 1, circuit 1 (DB), BJB face side, and the clockspring C218a-11, circuit 1 (DB), harness side.
    • Is the resistance less than 5 ohms? 
    1. YES  : Go to  A7.
    2. NO  : REPAIR the circuit. TEST the system for normal operation.
  7. A7 CHECK CIRCUIT 460 (YE/LB) FOR AN OPEN 
      Fig 6: Checking Horn Clockspring Circuit
      GF0014488Courtesy of FORD MOTOR CO.
    • Measure the resistance between the clockspring C218a-16, circuit 460 (YE/LB), harness side and ground.
    • Is the resistance less than 5 ohms? 
    1. YES  : Go to  A8.
    2. NO  : REPAIR the circuit. TEST the system for normal operation.
  8. A8 CHECK THE CLOCKSPRING 
    • Remove the driver air bag module. Refer to REMOVAL AND INSTALLATION article.
    • Disconnect: Upper Clockspring C218b
      • Fig 7: Checking Horn Clockspring Circuits
      GF0014489Courtesy of FORD MOTOR CO.
    • Measure the resistance between the upper clockspring C218b pin 5, component side, and the clockspring C218a pin 11, component side; and between the upper clockspring C218b pin 1, component side, and the clockspring C218a pin 16, component side.
    • Are the resistances less than 5 ohms? 
    1. YES  : Go to  A9.
    2. NO  : INSTALL a new clockspring and INSTALL the driver air bag module. REFER to REMOVAL AND INSTALLATION article. TEST the system for normal operation.
  9. A9 CHECK THE STEERING WHEEL SWITCH HARNESS 
    • Inspect the steering wheel switch harness for opens and shorts.
    • Is the steering wheel switch harness OK? 
    1. YES  : INSTALL a new driver air bag module or a new steering wheel, as necessary. REFER to REMOVAL AND INSTALLATION article for the driver air bag module, or REMOVAL & INSTALLATION article for the steering wheel. TEST the system for normal operation.
    2. NO  : INSTALL a new steering wheel switch harness. INSTALL the driver air bag module. REFER to REMOVAL AND INSTALLATION article. TEST the system for normal operation.
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