This is standard on many Pipers, 28Rs,32Rs, Senecas etc.
As squealing pig says, they are not off, but dimmed and therefore not noticeable in sunlight.
When you select gear down and you don't subsequently get the 3 greens, always ensure the nav lights are off, before adopting headless chicken mode
(Its a classic instructors trick to quietly switch the nav lights on and then await the student's reaction in due course.)