Be closely attuned or responsive, as in He couldn't make any important social connections because he just wasn't plugged in. The related expression be plugged into takes an object, as in These connoisseurs are plugged into the local art scene. These terms allude to inserting a plug into an electrical socket. [Colloquial; c. 1970]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.