Checking Lighting and Peripheral Systems

When checking lighting and peripheral systems, be sure to work in a systematic manner to avoid missing a faulty bulb or other component. A vehicle may have warning lights that will activate only if that circuit is in use. You may need to turn that circuit on to see the warning light. If you are unsure of where these are, ask your supervisor.

To check lighting and peripheral systems, follow the steps in Skill Drill 39-1:

In a darkened area, turn on or activate the ignition. The dash warning lights should be displayed. Start the engine. If any warning light stays on after the engine is started, it could indicate a problem in one of the vehicle’s safety or mechanical systems. If you are unsure about what any of the warning lights mean, consult the owner’s manual.
Make sure the vehicle’s horn is working. If the horn is not working, locate it under the hood with the help of manufacturer’s information. Check the wiring to make sure there is a good contact. If necessary, use a wiring diagram and DVOM to isolate the fault.
Have someone stand behind the vehicle to report any problems. Turn the ignition to run. Switch on the park lights, taillights, marker lights, and license plate lights. Do the same for left and right turn indicator lights. Depress the brake pedal to make sure the brake lights work and have the proper intensity. Also, place the transmission in reverse and check the back-up lights.
With someone in front of the vehicle, make sure the high and low headlight beams, park lights, turn signals, driving lights, fog lights, and cornering lights are all working properly.
With the interior light switch in the correct position, open the driver’s side door to make sure the interior lights work.
If any of these lights do not operate, you may need to replace a bulb, or diagnose the fault.