disabling power points when ignition switch is off?

i have a 2002 chevy silverado 2500 hd. the two powerpoints are on all the time. as i don't want to drain the battery down i would like them to go off when the ignition switch is off. i've been told by another person who owned one before that there is a way to jumper between two terminals in the underhood fuse block with a jumper wire with a fuse block in it that will do this