there are 2 other ways to do it
there are spade connectors that piggy back an extra spade lug that can be connected to the rear of the fuse block
also there are 3 triple plugs under the dash that use the bullet connectors , if I remeber right the yellow plug is constant power , the red plug is switched power & the orange is dash lights , all of these are there specifically to add accories or extra circuits ... too bad stereo installers never figure that out instead of just hacking into the harnesses