Ford Mustang (1999-2004) Service Manual: Horn (Diagnosis and Testing)

Refer to Wiring Diagrams Cell 44 , Horns/Cigar Lighter for schematic and connector information.

Special Tool(s)

73 Digital Multimeter or equivalent 105-R0051

Inspection and Verification

1. Verify the customer concern by operating the horn (13832).

2. Visually inspect for obvious signs of mechanical and electrical damage.

Visual Inspection Chart

Mechanical Electrical
  • Damaged horns
  • Damaged horn switch
  • Damaged air bag sliding contact (14A664)
  • Blown battery junction box (BJB) Fuse Horn Relay (20A)
  • Damaged wiring harness
  • Damaged connections
  • Damaged horn relay
  • Damaged horn switch

3. If fault is not visually evident, determine the symptom and proceed to Symptom Chart.

Symptom Chart

Condition Possible Sources Action
  • The horn does not sound
  • BJB Fuse Horn Relay (20A).
  • Circuitry.
  • Horn relay.
  • Air bag sliding contact.
  • Horn switch.
  • Horns.
  • GO to Pinpoint Test A .
  • The horn sounds continuously
  • Circuitry.
  • Horn relay.
  • Remote entry system (generic electronic module [GEM]) module.
  • Horn switch
  • GO to Pinpoint Test B .

Pinpoint Tests

PINPOINT TEST A: THE HORN DOES NOT SOUND

Test Step Result / Action to Take
A1 CHECK POWER SUPPLY TO HORN RELAY Yes

GO to A2 .

No

REPAIR the circuit in question. TEST the system for normal operation.
  • Disconnect: Horn Relay.
  • Measure the voltage between the horn relay connector Pin 2, Circuit 460 (YE/LB), harness side and ground; and between the horn relay connector Pin 5, Circuit 460 (YE/LB), harness side and ground.

  • Are the voltages greater than 10 volts?
A2 CHECK HORN RELAY Yes

GO to A3 .

No

INSTALL a new horn relay. TEST the system for normal operation.
  • Check the horn relay; refer to Wiring Diagrams Cell 149.
  • Is the horn relay OK?
A3 CHECK HORN SWITCH SIGNAL TO HORN RELAY Yes

GO to A4 .

No

GO to A5 .
  • Measure the resistance between horn relay connector Pin 1, Circuit 6 (YE/LG), harness side and ground under the following conditions:

Horn Switch Position

  • Are the resistances correct?
A4 CHECK WIRE BETWEEN HORN RELAY AND HORN Yes

INSTALL new horns.

TEST the system for normal operation.

No

REPAIR the circuit.

TEST the system for normal operation.
  • Key in OFF position.
  • Disconnect: Horn C1262.
  • Disconnect: Horn C1261.
  • Measure the resistance between the horn relay connector Pin 3, Circuit 1 (DB), harness side and horn C1261 or horn C1256 harness side; and between the horn relay connector Pin 3, Circuit 1 (DB), harness side and ground.

  • Is the resistance less than 5 ohms between the horn relay and the horns, and greater than 10,000 ohms between the horn relay and ground?
A5 CHECK WIRE BETWEEN HORN RELAY AND AIR BAG SLIDING CONTACT Yes

GO to A6 .

No

REPAIR the circuit.

TEST the system for normal operation.
  • Key in OFF position.
  • Deactivate the air bag system; refer to Section.
  • Disconnect: Air Bag Sliding Contact C218a.
  • Measure the resistance between air bag sliding contact C218a Pin 2, Circuit 6 (YE/LG), harness side and horn relay connector Pin 1, Circuit 6 (YE/LG) harness side.

  • Is the resistance less than 5 ohms?
A6 CHECK AIR BAG SLIDING CONTACT Yes

GO to A7 .

No

INSTALL a new air bag sliding contact.

REFER to Section. TEST the system for normal operation.
  • Disconnect the steering wheel switch harness from the air bag sliding contact.
  • Measure the resistance between upper air bag sliding contact connector Pin 3, Circuit 6 (component side), and air bag sliding contact C218a Pin 2, Circuit 6 (component side).

  • Is the resistance less than 5 ohms?
A7 CHECK THE STEERING WHEEL SWITCH HARNESS Yes

INSTALL a new horn switch. REFER to Switch-Horn . TEST the system for normal operation.

No

INSTALL a new steering wheel switch harness. TEST the system for normal operation.
  • Inspect the steering wheel switch harness for chafing, opens or possible short to ground.
  • Is the steering wheel switch harness OK?

PINPOINT TEST B: THE HORN SOUNDS CONTINUOUSLY

Test Step Result / Action to Take
B1 CHECK HORN CIRCUIT 1 (DB) Yes

REPAIR Circuit 1 (DB) for short to battery. TEST the system for normal operation.

No

GO to B2 .
  • Key in OFF position.
  • Disconnect: Horn Relay.
  • Does the horn continue to sound?
B2 CHECK HORN RELAY Yes

REINSTALL the horn relay. GO to B3 .

No

INSTALL a new horn relay. TEST the system for normal operation.
  • Check the horn relay; refer to Wiring Diagrams Cell 149.
  • Is the horn relay OK?
B3 CHECK CIRCUIT 6 (YE/LG) Yes

GO to B4 .

No

RECONNECT the air bag sliding contact. GO to B5 .
  • Disconnect: Air Bag Sliding Contact C218a .
  • Does the horn continue to sound?
B4 CHECK GEM INPUT Yes

REPAIR Circuit 6 (YE/LG). TEST the system for normal operation.

No

INSTALL a new GEM; REFER to Section.

TEST the system for normal operation.
  • Disconnect: GEM C201e
B5 CHECK THE AIR BAG SLIDING CONTACT Yes

INSTALL a new air bag sliding contact. REFER to Section. TEST the system for normal operation.

No

GO to B6 .
  • Deactivate the air bag system. Refer to Section.
  • Disconnect the steering wheel switch harness from the air bag sliding contact.
  • Does the horn continue to sound?
B6 CHECK STEERING WHEEL SWITCH HARNESS Yes

INSTALL a new horn switch. REFER to Switch- Horn . TEST the system for normal operation.

No

INSTALL a new steering wheel switch harness.

TEST the system for normal operation.
  • Inspect the steering wheel switch harness for shorts, opens, or any damage.
  • Is the steering wheel switch harness OK?
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