What would one of these do in relation to an install ?
http://www.crutchfield.com/S-ChXe4SzTJeL/cgi-bin/prodview.asp?i=120E5000

"The Bosch E5000 single pole-double throw (SPDT) relay is used in car security installations, primarily for interfacing with starter interrupt, door lock/unlock, and trunk release."

ClueLess

 

Its a standard relay. it has hundreds of uses. maybe you could be more specific

 

in some cars there are single wire controlled door locks that need a relay to complete locking procedures.....a relay for this job would look like this
http://www.velocitymotorsport.com/images/install_notes/244.jpg

 

Thanks, That kinda answered it :P..

 

just one instance as an example where u would use one