For those who have older Audi with AMI (Audi Music Interface) unit installed, we tend to get stuck with a 30-pin iPod and iPhone original AMI cables. There are many part numbers for each type and year of the car, but by playing and modifying AMI cables, I found out that they’re basically the same, the only thing different is the resistors detection. All 3G cables have detection resistor (pin21 & pin22) ~18.7k and 2G ~ 1.87k. When the resistor detection is less than 900 ohm – 0 ohm, the AMI changes to Auxiliary mode which will turn off the USB power and play whatever on pins 1,2 with ground 3. By design, the resistor detection will go to Auxiliary mode with value of 1k ohms for all version.
To make an external USB drive connector.
We need to get a female USB connector and wired it to the AMI connector with correct pins and designation: pin 28 (orange) = 5V, pin 25 (black) = Ground, pin 17 (green) = USB data +, pin 18 (yellow) = USB data -.
To make an Auxiliary Female Connector.
We need a female 3.5 mm jack connector: pin 1 (light brown) to left, pin 2 (purple) to right, and pin 3 (dark brown) to ground. It doesn’t really matter which pin 1 or 2 is left or right, as long as pin 3 is to ground.
To make a USB female power cable for USB dongle and relay (auxiliary mode) power when plugged in.
Get a female to male USB extension or a bulk female, but it’s better to get the extension an try to splice out the 5V and Ground line for the relay.