Rybo, hope this helps;

Here is a list of wire colors for the 2001 model;
2001 Nissan Xterra Wire Colors
Wire/Function.....Color.....Location/Description.....Polarity

12 Volts.....White/black.....Ignition switch.....+

Accessory.....Red or red/yellow.....Ignition switch.....+

Ignition.....Black/white.....Ignition switch.....+

Starter.....Black/green or green/yellow.....Ignition switch.....+

Starter2.....Black/ yellow.....Ignition switch.....+

Brake Switch.....Brown/red.....At switch above brake pedal.....+

Dimmer.....Pink/black.....At any illuminated switch in dash.....+

Parking lights.....Blue/red.....Drivers kick panel.....+

Doorpin.....Red/black***.....Pin-9 on Smart entrance module**.....-

Factory Alarm arm.....Yellow****.....Pin-30 on Smart entrance module**.....-

Factory Disarm.....Yellow/red****.....Pin-31 on Smart entrance module**.....-

Hand Brake.....Yellow or gray/blue.....At switch on hand brake lever.....-

Headlights.....Red/black.....At steering column.....-

Hoodpin.....Black/pink.....Pin-29 on Smart entrance module**.....-

Rear hatch pin.....Common with doors

Horn.....Lt. Green/red.....At steering column.....-

Reverse lights.....Yellow/red.....In driver’s running board.....+

Tach.....Blue*.....At distributor front of engine*.....AC

Key sense.....White/green.....Pin-24 on Smart entrance module**.....+

Speed sense wire(VSS).....Green/black.....Pin-37 behind instrument cluster*****

Lock.....Lt Green/red.....Pin-18 on Smart entrance module**.....-

Unlock.....Brown.....Pin-19 on Smart entrance module**.....-

Driver Window up.....Blue.....At master switch.....Rev. pol

Driver Window Down.....Blue/black.....At master switch.....Rev. pol

Passenger Window up.....Blue/yellow.....At master switch.....Rev. pol

Passenger Window down.....Blue/white.....At master switch.....Rev. pol

Left Rear Window up.....Green/red.....At master switch.....Rev. pol

Left Rear Window down.....Green/yellow.....At master switch.....Rev. pol

Right Rear Window up.....Green/white.....At master switch.....Rev. pol

Right Rear Window Down.....Green/black.....At master switch.....Rev. pol

also;

Radio
Harness #1 (2001)

+12V.....Red/yellow
Acc......Green/red
Dimmer.....Blue/red
Front Left -.....Black/white
Front Left +.....Blue
Front Right -.....Black/red
Front Right +.....Brown

Harness #2

Right Rear -.....Black/pink
Right Rear +.....Orange
Left Rear -.....Black/yellow
Left Rear +.....Green

* Same for both 2.4L and 3.3L. Tach can also be referenced at Pin-3 on the ECM at front of center console
** Located above drivers kick panel
*** On models without power door locks, this wire can be found in the drivers kick panel.
**** These wires will also operate the door locks. Double pulse yellow/red for unlock.
***** Also found at Pin-7 of the ASCD module on the left side of the steering column.