Horn and Wiper/Washer System Diagnosis and Repair
Horn Circuits
Horn systems are simple but test good circuit reasoning: battery feed, fuse, horn relay, horn button (often grounding the relay coil), and the horn itself. Know that many horns are grounded through the steering column or a clock spring, so a failed clock spring can kill the horn and other column functions. Understand that a horn that sounds weak may have high resistance in the feed or ground, and that dual-horn systems are usually wired in parallel.
Wiper and Washer Systems
Candidates should understand wiper motor operation including low and high speed, park position, and intermittent (pulse) control. Know that the park switch inside the motor keeps the motor powered until it reaches the park position, so a wiper that stops mid-windshield often indicates a park switch or motor fault rather than the dash switch. Washer systems involve a pump motor, often controlled by the same stalk or a module, and a clogged nozzle or failed pump is a common cause of no spray.
Traps
A classic trap is a wiper that works on high but not low speed-this points to the switch or motor speed circuit, not a dead motor. Another is assuming a no-horn complaint is the horn itself when the relay or clock spring is at fault. Questions also test intermittent wiper modules and that some systems use a body control module to time the wiper, so diagnosis must include the module and its inputs.
Rule of Thumb
For no-horn, check for voltage at the horn with the button pressed; if present, the horn or its ground is bad-if absent, work backward through relay and button. For wipers, confirm the switch input and the park circuit before replacing the motor.