Hours is a normal variable on airplanes, tractors and buses, for example. Or in your case, a work truck that's part of a fleet. It's never reset, but is used for maintenance tracking. Oil changes are done according to hours, say every 50 hours, for example. Maintenance is recorded by the maintenance crew in a tech log ("Engine Log") and stays with the machine's maintainers for the life of the vehicle. The FAA doesn't permit the tech logs to fly with the plane, for example, so that they're recoverable in the event of a crash. When you buy a used farm tractor or airplane, the tech logs will be available for inspection.
The engine hours in a piston-engine airplanes are recorded by a Honeywell "Hobbs meter" which may be set to recorded only flight hours. Those are the hours that do the wear and tear, as they say. The rest of the hours, idling or taxiing, are irrelevant.