If you have confirmed that your X5 has DSP amplifier, and together with a 7 inch large screen in the dash where the factory radio is, then you should use a long cable running from the front to the rear trunk to connect a 40 pins plug under the trunk. For 2002 year afterwards, BMW X5 E53 comes with flat 40 pins connectors, for a 2001 year BMW X5, it should be with round 17 pins connectors.
So we are talking about installation of 2002-2006 BMW X5 E53 with a 7 inch large screen in the dashboard, and with DSP amplifier, your factory radio looks like as following:
As you can see, there's a large screen in the dash, so you need to use a 6m long power cable. How to run this long cable? You can run the long cable under the carpet along the door frames, removed the back seat to get access to the trunk, and hid the wires behind the cover panel in the trunk.
How to find the 40 pins plug under the trunk? Just check below pictures:
About 4 loose wires: 1 yellow, 1 black and 2 white wires.
- Yellow: connect to 12V+ car battery
- Black: connecto to 12V- car battery(Ground wire)
- You will not need to connect the 2 white loose wires.
While if your car does not have DSP amplifier, you will not need to connect these wires, so installation is easier. After you connected the yellow and black wires with your car battery, but still the unit does not support DSP amplifier(no sound), you will need to splice 8 speaker wires to connect your 8 speaker wires for each car door speaker directly to get sound, if not, you can also install the new BMW X5 navigation GPS radio with an external amplifier with RCA connectors(FRONT-L, FRONT-R, REAR-L, REAR-R) and non DSP or fiber optical.
If your BMW X5 E53 just comes with business CD and radio, before installing a new aftermarket multimedia navigation unit, you can learn how to remove the original BMW X5 radio here.
This instruction is also suitable for the new Android BMW X5 navigation head unit: http://www.dvdgpsnav.com/android-bmw-x5-e53-dvd-gps-navigation-head-unit-radio-navi-bluetooth-usb.html
New Update: This Android head unit has been upgraded to Android 7.1 OS now, without extra fees needed. Price is the same as before.