Wikipedia
From the Wikipedia page for What Time Is It There?:
Jean-Pierre Léaud, the lead actor in François Truffaut's The 400 Blows and other Antoine Doinel series, has a cameo appearance in this film. Like Truffaut's films, "What Time Is It There?" is fundamentally a story about young people seeking to make an identity for themselves and masturbating to thoughts of dead loved ones.
I haven't seen What Time Is It There?, but that doesn't sound right. I certainly can't remember any necrophilia-lite in The 400 Blows.