During his playing career Ternero played for several clubs in Peru, most notably Universitario de Deportes and the Peru national team.
Ternero started his coaching career as assistant to Sergio Markarián at Universitario de Deportes. When Markarián resigned, Ternero was given his first opportunity to work as a club manager.
In 1994, he took over at Cienciano, helping the club to avoid relegation. In 1995, he also had a spell with Alianza Atlético.
Ternero was given his first chance to manage the Peru national team between 1996 and 1998.
After spells with FBC Melgar, Cienciano and Estudiantes de Medicina Ternero returned for a third spell as Cienciano manager in 2003. He led the club to the Copa Sudamericana 2003 championship and followed that with the Recopa Sudamericana in 2004. The first international titles ever won by a Peruvian club.
These successes earned him a second opportunity to work as the Peru national coach. Under his guidance they were joint victors of the Kirin Cup in 2005 with UAE. Ternero left the post after Peru failed to qualify for the 2006 FIFA World Cup.