How to Wire a Head Unit for a 2005 Audi A4

Factory Stereo Removal
1. Open the vehicle's hood and disconnect the black-colored negative battery cable from the battery's negative terminal, indicated by a minus symbol, using a socket and ratchet.
2. Examine the original stereo and locate the two key slots, positioned beneath each control dial.
3. Insert both removal key into the key slots. Grasp both keys and pull the stereo out of the dash console opening. You may need to spread the keys in an outward fashion, while pulling, to keep from accidentally or prematurely releasing the keys during the removal process.
4. Disconnect the antenna and wiring connectors from the rear of the unit. Remove the original stereo from the vehicle.
Replacement Head Unit Preparation
5. Examine the wiring schematics for the replacement head unit and harness adapter. Remove the pre-cut insulated ends of each wire for the stereo's proprietary wiring connector and harness adapter; twist the wire ends with your fingers to prevent fraying.
6. Connect the corresponding wires from the stereo's wiring connector to the harness adapter, one at a time, according to the stereo and harness adapter diagrams, using butt connectors and a pair of wire crimps. Give each connection a slight tug to ensure a proper connection.
7. Wrap the collection of wires with electrical tape to form a single cable. Be sure to cut off the ends of any unused wires to prevent possible shorts; fold the unused wires away from the connectors before wrapping the all of the wire connections with electrical tape.
8. Remove the mounting sleeve from the new head unit's chassis, according to the instructions provided with the manufacturer. Assemble the stereo install kit, according to the product's specific instructions; be sure to use a flat-head screwdriver to bend the small tabs of the mounting sleeve against the inside portion of the mounting kit, as doing so will properly secure the sleeve to the kit.
9. Slide the replacement head unit into the opening of the mounting sleeve.
Installation
10. Connect the vehicle-side wiring connectors to the female end of the harness adapter.
11. Connect the antenna adapter to the vehicle's antenna cable.
12. Connect the proprietary wiring connector for the stereo, and the remaining end of the antenna adapter, to the rear of the replacement unit.
13. Slide the stereo and mounting kit into the dash console opening. Press on the sides of the mounting kit until the kit snaps in place.
14. Reconnect the negative battery cable to the battery.