needsinfo

As the title says i need help with a stereo install for a 99 ES300.

Backstory:
I bought a new stero for my firend's birthday and want to surprise him with it installed because his does not work. I do not own the car and want to make it as easy as possible for myself when i go install it on Friday.

What i bought:
Kenwood KDC-BT318U
http://www.sonicelectronix.com/item_...DC-BT318U.html

Metra 71-8112
Amazon.com : Metra 71-8112 15-Pin Reverse Factory Radio Harness for Select 1992-1999 Toyota/Lexus Vehicles : Vehicle Wiring Harnesses : Car Electronics Amazon.com : Metra 71-8112 15-Pin Reverse Factory Radio Harness for Select 1992-1999 Toyota/Lexus Vehicles : Vehicle Wiring Harnesses : Car Electronics
Metra 71-8112 amp integration?
Amazon.com : Metra 70-8112 Radio Wiring Harness for Toyota Amp Integration 15 Pin : Vehicle Wiring Harnesses : Car Electronics Amazon.com : Metra 70-8112 Radio Wiring Harness for Toyota Amp Integration 15 Pin : Vehicle Wiring Harnesses : Car Electronics
Scosche LS2081B / LS2081( install kit)
http://sonicelectronix.com/item_8694...=scsho3597613&

Questions:
1. Do all 99 ES300 have a factory amp? or is it just an upgrade? This is why i bought both wire harness.
2. If it does have a factory amp, do i need to bypass with and splicing or is the Metra 71-8112 amp integration enough?
3. On the wire harness,metra 71-8112, without the amp integration, there are only (+) speaker wires, but on the back of the unit there are both (+)(-) speakers wires. Will the unit work with just the (+) connected. Here's a diagram of the Metra 71-8112: http://www.metraonline.com/files/pro...NST71-8112.pdf

Any information would be helpful. Thank you.