Just thought I'd repost this one under a more searchable heading. Many of the newer Audi's are using more features on the CAN-BUS with their HU's, and thus "simplifying" wiring to the unit. Later models no longer seem to provide a separate remote on/ignition feed to the OEM HU, now adopting the CAN-BUS to send data to the HU to tell it that the ignition has been switched on, so please turn yourself on. What a great application of digital technology? As the old separate ignition supply really was showing its age /ubbthreads/images/graemlins/grin.gif So when replacing the old dog with something that works properly and sounds fantastic, you are forced to poke the "ignition on" wire into the permanent live, thus having to manually turn off your HU everytime you leave the vehicle, with the resultant flat battery if you forget. If this is the case on your vehicle you will see from the black ISO connector that you are missing a few wires. Traditionally there are 4 or more (perm live, ground, ignition, remote on/power antenna). If you only have 3 on this block then you will need to perform this mod. Firstly locate your fuse box (drivers side end of the dash), prise off the cover. The fuse you need to locate is either no. 37 or no. 10, (varies depending on year, check on the back of the fuse box cover as this seems to be tailored to the car, the manual is generic and not always accurate). The fuse you need to locate is described as S-contact (radio) and should be 10amps. Bear in mind the fuses are upside down and back to front as the manual is for LHD vehicles. When you locate it, pull it out, and check with a multimeter that 12v is present with the ignition on, but disappears when you pull the keys out. If you don't have a multimeter, buy one of those 12v testing screwdrivers (very useful for £2.99). Now you need to access the wiring to the fuse. Unscrew the 2 Torx screws holding in the fuse panel. The panel is now held in via a couple of plastic clips. You now need to remove the drivers side dash trim. This is fairly easy, 3 Torx screws on the end (around the fusebox), then 3 more detailed below. The trim unclips at the top either side of the steering wheel. Unclip the wiring for the headlights and manoevour over the bonnet release and out. The wire to the load side of the fuse seems to be consistently red with a white stripe, shown below. Just wire tap onto it and feed the wire back up to the HU's ignition on lead. You will now have a HU that turns off when you take the keys out, just like the OEM unit. The only difference being that you can't turn the HU on without the keys.