Final answer:
During a pre-trip inspection, check for variations in headlight intensity which can indicate changes in the vehicle's electrical load. Do not look directly at the lights to avoid eye damage. Observe indirectly or by looking at the light's reflection on a surface.
Step-by-step explanation:
When you check the headlights on your car during a pre-trip inspection, you should look for several indicators that they are functioning properly. If you turn on the low beams, high beams, and observe the four-way flashers and turn signals, you might notice that the intensity of the lights may vary. This variation can occur when there is a change in the electrical system's load, as seen when other components that draw power are activated.
For instance, when you start the engine of your car, the passenger compartment light may dim momentarily due to the initial power draw from the starter motor and possibly because of resistance within the battery. Similarly, if your car's headlight intensity changes when other electrical devices are used, it might be due to the overall demand on the car's electrical system; for example, when high-powered devices come on, like the air compressor or the radiator fan.
It is important to note that you should not look directly at the headlights since very bright light can be harmful to the eyes. Instead, check for changes in light intensity indirectly or by observing the light pattern on a garage door or wall.