If the OEM stereo is still currently installed then your (his) best bet would be to simply get a factory harness adapter to provide all of the necessary connections for the new headunit.
Said adapter just splices onto the wiring harness supplied with the new stereo, matching each wire color for color (red to red, black to black, yellow to yellow, green to green, green w/ black stripe to green with black stripe, etc etc so on and so forth).
Once all those connections are solidly made the whole affair simply snaps into the harness plugs already present behind the dash and you're done. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
These adapters are available at any car stereo shop, Best Buy, Circuit City, shoot - even WalMart! //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif