Where is the cabin air filter on a 2000 Ford F150 - if equipped?

A 2000 Ford F-150 did not come standard with a cabin air filter. It was not a common feature on trucks of that era. Some later model years started offering it as an option, and some aftermarket solutions were available, but it wasn't originally included in the design. Therefore, you won't find a factory-installed cabin air filter in the usual locations found in later vehicles.