I'm toying with the idea of a custom audio system for my XJ8. I've found a few threads about the standard audio headunit around here, but I still have a couple of questions I hope people can help with.

Firstly, there is a 6-pin DIN connector on the back of the headunit that's not connected on my model. Does anyone know what this is for? From the wiring diagram, it looks like it should be for the CD changer, but mine has a CD changer fitted and this is not connected (though admittedly I have no idea whether the CD changer works - don't have any CDs).

Secondly, as near as I can tell, pins 10 and 11 on connector IC10 (the 20-pin TE 282991-2 connector) are the power connection. Is that right? Both of them are marked B+ on the schematic - is there any difference between them?

Thirdly, pin 5 of IC10 is marked as the antenna motor control. What does the headunit do with this wire to make the antenna extend / retract?

Fourthly, pin 2 of IC10 is marked as the interface to the steering wheel controls. I think how this works is that you apply a voltage at IC10 pin 2 and then measure the current it draws - the buttons each have a different resistor attached, and so by measuring the current, you can tell which button was pressed. Have I got that right?

Fifthly, IC10 pin 1 is marked as the vehicle speed measurement. As near as I can tell, this is a pulse train corresponding to the vehicle speed. Does anyone know (a) what voltage this is and (b) how to convert the pulse train to a speed measurement? Is it a pulse-per-revolution system, or is it pulse width modulated?

Thanks for any help,
Tom