North from where? You may be better off getting on the Harbor Freeway northbound, depending on how far south of downtown, you are.
If you do take the 405, go north to the Santa Monica Freeway (10), west, to the Harbor Freeway, north. Immediately look for freeway signs indicating the Convention Center.
I'll be back with a map url in a sec, if I can find one quickly.
Wassup @ the Convention Center, today?