Texas Transportation Code § 547.501. Audible Warning Devices -
(a) A motor vehicle shall be equipped with a horn in good working condition that emits a sound audible under normal conditions at a distance of at least 200 feet.
(b) A vehicle may not be equipped with and a person may not use on a vehicle a siren, whistle, or bell unless the vehicle is:
(1) a commercial vehicle that is equipped with a theft alarm signal device arranged so that the device cannot be used as an ordinary warning signal; or
(2) an authorized emergency vehicle that is equipped with a siren, whistle, or bell that complies with Section 547.702.
(c) A motor vehicle operator shall use a horn to provide audible warning only when necessary to insure safe operation.
(d) A warning device, including a horn, may not emit an unreasonably loud or harsh sound or a whistle.This is what in the traffic code in Texas, Inspection is a different animal.....
A Train horn is very different from a Truck horn. Truck horns are usually around 90-110 DB and train horns are required to be more than 120 db if I recall. The inspector is either new and full of himself or just misinformed either way he's wrong, motorhomes don't have train horns they have truck horns. There is probably a definition in the code somewhere but I'll let someone else find it.