Yes, you will need 2 harnesses. 1 for the steering wheel and 1 for the JBL amp.
If you go to Crutchfield and put in your vehicle information, they will have a list of accessories you will need for your install.
I recently installed the Sony XAV-AX5000, is this what you are looking for?
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-2004 4Runner Limited 2WD, V8
Bilstein 5100s/MOOG FJ Springs, GROM USB/Bluetooth, Fosgate Sub/AMP Upgrade, Hankook Dynapro AT 265/70-17
-1999 4Runner SR5 2WD, V6
205,000 miles, Tundra Brake Mod (Daughter rolled over and totaled, but she walked away)