Good point on the speaker wires. With the JBL system, the speaker wires terminate at the amp under the seat, and without at the HU. Seems like this would be a major project. To get the needed harnesses, you will probably have to get them from Toyota, doubt anyone is going to remove them when upgrading their system.
It is not just one harness, there are going to be completely different harnesses at the head unit, you will also have to require all of your speakers and add quite a bit of wiring, its not just a simple harness from deck to amp, it can definitely be done (anything can be done) but it will not be fast nor easy. Ill put it this way. I have been a professional car electronics installer for 22 years and it would be a 12-18 hour project for me. It is also going to cost substantially more than a compete aftermarket sound system, but if you are comfortable with all of that them more power to you. I am by no means trying to Piss in your Cheerios just want you to know going in that its not going to be a simple plug and play sound system install, you should be able to source most of the parts used but the wire harnesses aren't going to be easy to find. They don't run alone in the trucks, there are many other wires in the same harnesses so people don't pull the wiring when replacing the jbl system.. You'll probably have to get those from the dealership or junk yard.From reading all the posts about how hard this is I'm guessing no one has actually done it before. I'm determined to continue. I'll keep a record of all the part numbers and installation details and post them when I'm finished. Perhaps some else will want to do this.
In the mean time if anyone has any of the harnesses that I need, speakers or GPS antenna I'm interested. Also, if anyone knows the routes that the JBL harnesses take please let me know.
I'm interested in that photo of the JBL amp mounted under the seat.
2007 SR5 REG CAB