2000 maxima i replace the o2 sensor but the wire for the new sensor are red white and black the old has 2 whites 1 black 1 grey please is driving me nuts

Sounds like the new one you bought is for the front O2 sensors or before the cat and the one you are wanting to replace is on the back or after the cat. Hope this helps.

Are you sure that have 3 wires? For Nissan say 3 wires.

This is the alterative wire:
Signal + --->> Black -->> Black
Signal - --->>
Heater --->> White -->> Red
Heater --->>White -->> White

Review this information: Bosch Universal O2 Sensor (check the Universal sensor types and color identification )

Hope helped with this (remember rated this help) God luck.

The paperwork with the bosch o2 sensors should have a wiring diagram for splicing the wires.