There are two suggest ways to get a ride on the cable cars.  If you want to be "car-free", just walk down to the corner of Stanyan and Carl and take the N Judah train heading inbound to Union Square.  Once off, look for the Powell Street cable car - this will take you up and down some classic San Francisco hills and ultimately bring you to Fishermans' Wharf.  The other way is to just drive your car to Fisherman's Wharf, downtown, or Union Square, park the car, and jump on the cable cars.

 
Cable Car Info 04/27/2008
 


All you want to know is here:

http://www.sfcablecar.com/

 
 

From Parnassus Heights, you can either take a cab and get there in about 15 minutes or you can enjoy two San Francisco attractions in one trip by taking first the N Judah to Union Square (the Powell stop) and then get on the Powell cable car and take that to Fisherman's Wharf.  Allow for as much as 45 minutes in case you spend time waiting for either the train or cable car to arrive.