The Heater is non polarized.
Never use an ohm meter to measure the signal wire , in any way or you WILL blow the CELL up.
The below table is the actual sensor colors and is NOT the vehicle harness wire colors.!
If you miswire the Signal to the heater, the O2 sensor will be blown out!

NGK MFG LIST

NGK PDF HOW TO INSTRUCTIONS.
 

O2  Sensor ?

SIGNAL

GROUND

HEATER

HEATER

AC DELCO

PURPLE

TAN

BROWN

BROWN

BOSCH

BLACK

GREY

WHITE

WHITE

BWD 1

BLACK

GREY

WHITE

WHITE

BWD 2

PURPLE

GREY

WHITE

WHITE

BWD 3

PURPLE

TAN

BROWN

BROWN

DELPHI 1

PURPLE

TAN

BROWN

BROWN

DELPHI 2

BLACK

GREY

PURPLE

WHITE

DENSO

BLUE

WHITE

BLACK

BLACK

HONDA 1

WHITE

GREEN

BLACK

BLACK

HONDA 2

BLUE

WHITE

BLACK

BLACK

NGK

BLACK

GREY

WHITE

WHITE

SMP/STD

BLACK

GREY

WHITE

WHITE

TOYOTA

BLUE

WHITE

BLACK

BLACK
Suzuki Sidekicks
  BLUE
 White
 Black
 Black

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