power source question

I am planning a video system install for my 2001 Chevrolet Tahoe.

The system will consist of a 400W Inv, PS2, Video amp & (3) monitors.  I installed a P.I.E. aux input adapter for audio through the factory HU & it works great (retained OnStar, etc.).

My question is...Instead of pulling a wire from the battery through the firewall, can I use a source already inside the cabin?  My Tahoe does not have power seats.  However, in the instrument panel fuse block, there is a 25A power seat circuit breaker.  Is there an appropriate way to use power from the fuse block (through a relay) for the inv?  I also noticed (in a second utility panel under the dash) that there are unused sockets.  Would power be available from any of them?  A simple block diagram of my thoughts is attached.  The add-a-circuit(s) will be connected to circuit(s) powered with the radio (Retained Accessory Power).  I would just prefer to use a power source without having to push a wire through an already tight bundle of wires through the firewall.

I have had no luck in searches for valuable info on my Tahoe's electrical distribution.  I appreciate any info/insight that can be offered.

Thanks for the reply, Teken.

I have the load info for each piece of the system.  Under 1A for each piece (monitors, video amp).  My plan is to add a 5A circuit to an existing circuit that has the appropriate switching.  The inverter on the other hand can handle loads up to a total of 320W continuously.  The PlayStation2 is an 80W load.  I will occasionally also use the inv to charge dig camera batteries, charge cell phone maybe, etc. (small loads only).  I plan to energize the relay carrying power to the inv with another circuit with the appropriate switching.  Possibly split the load of all monitors, video amp and relay to minimize load on each circuit.

I am in hopes that someone will have specific information on the Tahoe's power distribution and I'll be able to find an appropriate power source based on the info.  Hopefully, someone can also offer info on AWG of the factory conductors.  If this info is not offered through the forum, where can I obtain it (most economically)?

That said...you may be right Teken.  I'll probably end up running a wire from the battery through the firewall.  Any advice on how to best do it?  I have never and don't want to ruin the factory seal around the existing run or skin a wire trying to push another one through the opening that seems to be really tight.

 WRT the Tahoe wiring, see if a local shop uses ALLDATA information services.. they should be able to pull the entire wiring harness diagrams.

 My suggestion would be to pull a feed off the battery for all this... that inverter can draw over 30 amps @ full load.

 Regards,

 Jim