ASE G1 Auto Maintenance and Light RepairElectrical/Electronic SystemsHard
A vehicle's horn is inoperative. When the horn button is pressed, no sound is heard, and a test light connected to the horn's power wire illuminates brightly. What is the MOST likely cause?
- AA low battery voltage
- BA short circuit in the horn button
- CAn open circuit in the horn's ground wire
- DA faulty horn relay
Show answer & explanationAnswer & explanation
Correct answer: C. An open circuit in the horn's ground wire
If the test light illuminates brightly when connected to the horn's power wire, it confirms that power is reaching the horn. Since no sound is heard, the problem is likely with the other side of the circuit, which is typically the ground. An open circuit in the ground wire would prevent the horn from completing its circuit and sounding, despite having power.
Why the other options are wrong
- A. Low battery voltage might make the horn sound weak or not at all, but the test light indicating 'brightly' suggests sufficient voltage is reaching the horn, ruling out low battery as the primary cause here.
- B. A short circuit in the horn button would likely cause the horn to sound continuously (if it's a ground-activated button) or blow a fuse, not prevent it from working while power is present at the horn.
- D. If the horn relay was faulty and preventing power from reaching the horn, the test light would not illuminate brightly at the horn's power wire.
Horn Circuit Diagnosis (No Ground)
If power is present at the horn, but it doesn't sound, the fault is likely an open in the ground circuit, preventing current flow completion.
- Verify power first.
- Horn needs both power and ground.
- Open ground prevents circuit completion.
Memory trick: Horn's Got Power, But No Sound? Check the Ground!