During a pre-trip inspection, if the electric horn does not work, what should you verify next?

Verifying the air horn after discovering that the electric horn is not functioning is an important step during a pre-trip inspection. Both horns serve the critical safety function of alerting other drivers and pedestrians, and they may operate on different systems. By checking the air horn, you can determine whether the issue lies solely with the electric horn or if there could be a broader problem with the vehicle's horn system. If the air horn works, it suggests the electric horn has a specific fault rather than a complete failure of the horn system. This systematic checking ensures that all safety measures are in place before operating the vehicle, which is vital for safe driving conditions.

The other options do not address the immediate concern about the horn system. Inspecting the windshield wipers, disabling the vehicle, or looking at the heater does not help diagnose issues related to the vehicle's ability to sound alerts, which is critical for safety on the road.