newbie on board amp install question

[pucknut]

just jioned the saab community
bought a used 2004 9-3 linear
did the 90k service based on info from this forum thank you all
replaced all factory speaker added 6x9s in the rear now need to go thru the firewall to add the amp
i know some will say use the hook ups for the optional amp in the trunk
given all the electrical issues i would rather go thru the firewall
can someone please point to a walkthru
i search and could not find on this site
could be i am not navigating properly
any and all info and links appreciated
many thanks

[boostpowered]

run through the grommet the vaccume line runs through or you can remove the dash and go through any of the wiring grommets

[pucknut]

can you tell me where the vacum lines lead
i checked there and it looks like i have to remove the dash or head unit
some say go thru the steering boot but thats seems weired
i am probably thick but can you orientate me more
many thanks

[boostpowered]

look above your left foot if not there get under dash with a flshlight and search