§393.25 incorporates the lamp-mounting and operability requirements applicable to head lamps as set out in §393.9 and the related FMVSS 108 specifications. Head lamps must be mounted, aimed, and operational; the rule is enforced through §393.9, which generically prohibits required lamps from being inoperable.
OOS
Inoperable head lamps when the vehicle is operated between sunset and sunrise (or when reduced visibility requires lamps under state law) is an OOS condition under the NAS Out-of-Service Criteria. The vehicle may not continue until the head lamp is repaired.
Severity weight
Severity weight 6 in the Vehicle Maintenance BASIC. The weight is high relative to other lighting findings (§393.9 inoperable lamp is typically 6 or lower depending on the lamp type) because head-lamp failure is associated with direct crash risk.
How to prevent it
- Make head-lamp verification a pre-trip non-negotiable, including high-beam check.
- Replace both head lamps in pairs even when only one has failed — second failure usually follows within weeks.
- Aim and adjust per FMVSS 108 after any front-end repair.
How Roadworthy HQ helps
§393.25 / §393.9 head-lamp findings logged in Roadworthy HQ link to the vehicle and block dispatch under §396.11(c) until the §396.9(d)(3) repair certification is on file.