Finally, I can install the head unit. I'm using an Alpine IVA-D105 multi-media unit.

Since I cannot install my own amplifiers, I have to use the JBL for now. I bought a Axxess TYTO-01 level shifter/harness to connect the two together. You can see it here along with the zillion wires from the head:



The navigation unit needs a connection to the speed sensor. Again looking in the schematics, I find it conveniently is located in one of the harnesses that was connected to the JBL:



It is pin 4 of connecter K9. Looks like this:





Also required from the JBL harness is the connections for the steering wheel controls. The schematic shows it to be pins 6,7 and 8 on connecter K3 (brown, light green and grey):





The steering wheel interface unit says to install a 560 ohm resistor between pins 7 and 8:



Don't think I mentioned it earlier but all spliced connections are protected with heat shrink:



.