Rule of thumb: if a vehicle must be registered for use on public roads, its liability belongs on an auto policy, not a homeowners policy.
Excluded: liability arising from the ownership, maintenance or use of motor vehicles that must be registered for road use, such as the family car, a pickup or a motorcycle. The exclusion applies even when the driver is an insured, for example a resident teenage son driving the family car to school.
Typically still covered:
A vehicle not required to be registered that is used to service the residence, such as a riding lawn mower.
A recreational vehicle the insured owns, such as a dirt bike, but generally only while it is on an insured location, not on trails miles from home.
Homeowners liability does not sit on top of an auto policy as excess coverage. A household that wants more protection above its auto liability limits buys an umbrella policy.