How can I switch to an external db with Views API?
Sounds as if you need the Views Database Connector module.

From the project page:


  Views Database Connector is a powerful module that gives Views full access to external database tables found in the settings for your Drupal installation. With this module, you can setup a view around any table in any database configuration. This can be extremely useful to pull external data from a database to show to your users in a view.