o2 sensor QR25DE

[SlammedAC08]

this is probably a stupid question but I've been searching for the answer for about a week. So here is my question to you guys. The o2 sensor on the exhaust manifold has four (4) wires two black one white one blue. now which one of these wires is the signal wire? thanks for you help.

[SlammedAC08]

for those of you who have the same question; the blue wire is the signal wire, the black wires are 12v heater wires.

[QR25DE]

Out of curiosity why did you need the info? Project in the works?