Jrod,
Welcome to the site and congrats on getting the 4runner. I have a 2008 and had the JBL system with Nav, factory backup cam and did the Scion swap. I had the same experience as most people posting on here did not have our setup. With that said, I installed the Scion unit. It is fairly straightforward and everything works great.
The first Metra TYTO adapter crapped out after a month and half. I returned it through Amazon and the replacement has been going strong for the last 7 months.
Here is a list of parts that I think is correct:
• Metra TYTO-01- Converts the analog output of the head unit to the digital signals the Synthesis amp is looking for.
• 71-1761- Reverse Wiring Harness- Allows you to plug the converter into the Scion head unit without hacking up any vehicle wiring.
• 28 pin harness- PT546-00120-CH
• Antenna Adapter- PT546-00120-AD
• and if you want Bluetooth PT546-74120-MC
• and USB- PT546-00120-US
• you will need a Y-harness for the two radio antennas if you want HD radio. I only put one in and lose HD when the vehicle moves. you only need one if you just want radio
• antenna adapter because the connectors are different sizes
If you have the factory backup camera, you can buy a harness from autoharnesshouse.com or you can use the one from the JBL system. You may also need a wire with a pin to plug into an empty slot on the harness to get the VSS “speed sense” for the navigation. It is on the pin diagram floating around here. It is the middle wire #3 on the 6-pin R-9 harness where the reverse is also located. That goes into pin #17 on the 28-pin harness on the FRS radio. If the "reverse" wire is on the top row, second in from right, the VSS or (SPD) is one the row below, 3rd pin in from the right.
Here is a diagram that may help
You will need a wire with the proper connector to push into the existing harness. You can try a local stereo shop. I ordered one from autoharnesshouse.com. Brian is very helpful and responds to emails. Ultimately, you need two separate wires , one with the male connector ends and one with the female to get the reverse and the VSS to work. Brian will sell you both. Get those and you are done. Also, if you don't want to cut the factory wires, he will sell you the connector that hooks into the R-9 connector with the two wires out for the reverse and VSS. Then you just push the other ends into the corresponding pin holes and you are done.
You only need the USB if you want to be able to connect to the unit via USB. I just use Bluetooth and never use the USB I installed. To put the mic in for the Bluetooth is simple. I mounted on top of the steering column and used my heat gun to heat the glue on the double-sided tape. Holds like concrete.
Anyway, hit me up if you have any questions.
I meant to do a tutorial on this, but it never happened. I do have pictures if you need them.
Squ1d