This is an attempt to collect information about all factory radios, their interchangeability and aftermarket replacement instructions in one place.
Any comments, corrections or suggestions are appreciated.
All 2005-2008 models and 2005-2013 X model come with double DIN sized OEM head units that can be easily replaced by an aftermarket radio.
2005-2007 X and S
Double DIN AM/FM/CD radio
Connectors: 10+6 pin "old type" dual connector
Aftermarket harness: Metra 71-7550 or Scosche NN03B
2005-2008 SE and Pro-4X
Rockford Fosgate system with a double DIN 6CD MP3 head unit and external amplifier
Connectors: 10+6 pin "old type" connector with two smaller connectors for sat radio and steering controls
Aftermarket harness: Metra 71-7551 or Scosche NN07B
2008 S, 2008-2013 X
Updated base radio
Connectors: single 20-pin "new type" connector
Aftermarket harness: Metra 71-7552 / Scosche NN04B + Metra 40-NI12 antenna adapter
2009-2012 S and Pro-4X radios are integrated into the center dash panel
2009-2012 S
Base radio
P/N: 28185-ZL05A (2009-2010), 28185-9CH0A(2011-2012)
Connectors: single 20-pin "new type" connector
Aftermarket replacement:
Metra 71-7552 or Scosche NN04B harness
Metra 40-NI12 antenna adapter
Metra 99-7428B or Scosche NN1661B dash kit
2009-2012 Pro-4X
Rockford Fosgate system with 6CD MP3 head unit, external amplifier, XM and Bluetooth
P/N: 28185-ZL45A or 28185 9BH5A (head unit), 28388 9CA1A (Bluetooth), 28051 EH00B (XM tuner)
Connectors: 10+6 pin "old type" and two smaller connectors for sat radio, steering controls and bluetooth
Aftermarket replacement:
Metra 71-7551 or Scosche NN07B harness
Metra 99-7428B or Scosche NN1661B dash kit
2013+ models (2014+ for X) have redesigned center dash panel with a slightly larger than 2DIN slot for the head unit. An extra button was added to the steering wheel controls.
2014-2015 X
New basic radio with Bluetooth but no USB
P/N: 28185-9BK0A
Connectors: 20-pin and 16-pin connector for Bluetooth module and steering controls.
Aftermarket replacement:
Metra 71-7552 or Scosche NN04B harness
Metra 40-NI12 antenna adapter
Metra 99-7619 or 95-7619 dash kit
2013-2014 S
Color display radio with USB, Bluetooth and XM. XM tuner is integrated into the head unit, but Bluetooth module is external. Made by Panasonic.
P/N: 28185-9FM1A (head unit), 28388-9GF0A (Bluetooth)
Connectors: 20-pin and 32-pin connector for Bluetooth module and steering controls
Aftermarket replacement:
Metra 71-7552 or Scosche NN04B harness
Metra 40-NI12 antenna adapter
Metra 99-7619 or 95-7619 dash kit
AX-NISUSB-2 or Scosche NNUSB02B USB retention adapter
2015 S
Updated color display radio with Mobile Apps, USB, Bluetooth and XM.
P/N: 28185-9BK1A
Connectors: 20-pin and 32-pin connector for Bluetooth module and steering controls
Aftermarket replacement:
Metra 71-7552 or Scosche NN04B harness
Metra 40-NI12 antenna adapter
Metra 99-7619 or 95-7619 dash kit
2013 Pro-4X
Nissan Connect navigation system (Bosch LCN2) with external Rockford Fosgate amplifier
P/N: 25915-9FM0B
Connectors: 20-pin and 24-pin connector for microphone, camera, steering controls, etc.
Aftermarket replacement:
Metra 70-7553 or or Scosche NN05B main harness
Metra 40-NI12 antenna adapter
Metra 99-7619 or 95-7619 dash kit
AX-NIS32SWC steering wheel controls and camera retention adapter
AX-NISUSB-2 or Scosche NNUSB02B USB retention adapter
2014-2015 Pro-4X
Nissan Connect Navigation with Mobile Apps (Bosch LCN2kai) with external Rockford Fosgate amplifier
P/N: 25915-9CJ0A (2014), 25915-9CJ1A (2015)
Connectors: 20-pin and 24-pin connector for microphone, camera, steering controls, etc.
Aftermarket replacement:
Metra 70-7553 or Scosche NN05B main harness
Metra 40-NI12 antenna adapter
Metra 99-7619 or 95-7619 dash kit
AX-NIS32SWC steering wheel controls and camera retention adapter
AX-NISUSB-2 or Scosche NNUSB02B USB retention adapter (only for 2014)
Wiring diagrams
Factory service manuals with diagrams and pinouts of all OEM radios are available here:
http://www.nicoclub.com/archives/nissan-xterra-factory-service-manuals.html
Choose your model year and select "av.pdf"
Any comments, corrections or suggestions are appreciated.
All 2005-2008 models and 2005-2013 X model come with double DIN sized OEM head units that can be easily replaced by an aftermarket radio.
2005-2007 X and S
Double DIN AM/FM/CD radio
Connectors: 10+6 pin "old type" dual connector
Aftermarket harness: Metra 71-7550 or Scosche NN03B

2005-2008 SE and Pro-4X
Rockford Fosgate system with a double DIN 6CD MP3 head unit and external amplifier
Connectors: 10+6 pin "old type" connector with two smaller connectors for sat radio and steering controls
Aftermarket harness: Metra 71-7551 or Scosche NN07B

2008 S, 2008-2013 X
Updated base radio
Connectors: single 20-pin "new type" connector
Aftermarket harness: Metra 71-7552 / Scosche NN04B + Metra 40-NI12 antenna adapter

2009-2012 S and Pro-4X radios are integrated into the center dash panel
2009-2012 S
Base radio
P/N: 28185-ZL05A (2009-2010), 28185-9CH0A(2011-2012)
Connectors: single 20-pin "new type" connector
Aftermarket replacement:
Metra 71-7552 or Scosche NN04B harness
Metra 40-NI12 antenna adapter
Metra 99-7428B or Scosche NN1661B dash kit

2009-2012 Pro-4X
Rockford Fosgate system with 6CD MP3 head unit, external amplifier, XM and Bluetooth
P/N: 28185-ZL45A or 28185 9BH5A (head unit), 28388 9CA1A (Bluetooth), 28051 EH00B (XM tuner)
Connectors: 10+6 pin "old type" and two smaller connectors for sat radio, steering controls and bluetooth
Aftermarket replacement:
Metra 71-7551 or Scosche NN07B harness
Metra 99-7428B or Scosche NN1661B dash kit

2013+ models (2014+ for X) have redesigned center dash panel with a slightly larger than 2DIN slot for the head unit. An extra button was added to the steering wheel controls.
2014-2015 X
New basic radio with Bluetooth but no USB
P/N: 28185-9BK0A
Connectors: 20-pin and 16-pin connector for Bluetooth module and steering controls.
Aftermarket replacement:
Metra 71-7552 or Scosche NN04B harness
Metra 40-NI12 antenna adapter
Metra 99-7619 or 95-7619 dash kit

2013-2014 S
Color display radio with USB, Bluetooth and XM. XM tuner is integrated into the head unit, but Bluetooth module is external. Made by Panasonic.
P/N: 28185-9FM1A (head unit), 28388-9GF0A (Bluetooth)
Connectors: 20-pin and 32-pin connector for Bluetooth module and steering controls
Aftermarket replacement:
Metra 71-7552 or Scosche NN04B harness
Metra 40-NI12 antenna adapter
Metra 99-7619 or 95-7619 dash kit
AX-NISUSB-2 or Scosche NNUSB02B USB retention adapter

2015 S
Updated color display radio with Mobile Apps, USB, Bluetooth and XM.
P/N: 28185-9BK1A
Connectors: 20-pin and 32-pin connector for Bluetooth module and steering controls
Aftermarket replacement:
Metra 71-7552 or Scosche NN04B harness
Metra 40-NI12 antenna adapter
Metra 99-7619 or 95-7619 dash kit

2013 Pro-4X
Nissan Connect navigation system (Bosch LCN2) with external Rockford Fosgate amplifier
P/N: 25915-9FM0B
Connectors: 20-pin and 24-pin connector for microphone, camera, steering controls, etc.
Aftermarket replacement:
Metra 70-7553 or or Scosche NN05B main harness
Metra 40-NI12 antenna adapter
Metra 99-7619 or 95-7619 dash kit
AX-NIS32SWC steering wheel controls and camera retention adapter
AX-NISUSB-2 or Scosche NNUSB02B USB retention adapter

2014-2015 Pro-4X
Nissan Connect Navigation with Mobile Apps (Bosch LCN2kai) with external Rockford Fosgate amplifier
P/N: 25915-9CJ0A (2014), 25915-9CJ1A (2015)
Connectors: 20-pin and 24-pin connector for microphone, camera, steering controls, etc.
Aftermarket replacement:
Metra 70-7553 or Scosche NN05B main harness
Metra 40-NI12 antenna adapter
Metra 99-7619 or 95-7619 dash kit
AX-NIS32SWC steering wheel controls and camera retention adapter
AX-NISUSB-2 or Scosche NNUSB02B USB retention adapter (only for 2014)

Wiring diagrams
Factory service manuals with diagrams and pinouts of all OEM radios are available here:
http://www.nicoclub.com/archives/nissan-xterra-factory-service-manuals.html
Choose your model year and select "av.pdf"