Oxygen Sensor Wiring:
For 1g:
(From DSM Backup manual for 91 DOHC turbo)
Looking from the wire side, the harness round connector has pin 1 in upper left, 2 upper right, 3 lower left, 4 lower right. This would also be the way it looks on the sensor round connector if looking at the connector with the wires on it's opposite side. (Can also see here: http://www.dsmtuners.com/forums/bolt-tech/171244-o2-sensor-wiring.html#post1431571)
Harness side: Red (pin 3 - goes to MPI relay for power) and black (pin 4 - goes to ground) are for the heaters. White (pin 1 - goes to ECU pin 4) is signal. Black (pin 2) is signal ground (goes to engine ground on a 1g). The signal and signal ground are usually shielded.
Sensor side: Every aftermarket O2 has different color wires (http://www.academia.edu/5496281/O2_...from_http_www.hiflo.com.au_oxygen_sensors.cfm). The 2 same color wires, usually white (but sometimes black), are the heaters (go either polarity - they measure about 12 ohms so you can easily find them even if they are not the same color). The other 2 are the signal and signal ground wires. If black and grey, try the sensor black to harness white and sensor grey to harness black. If it doesn't work reverse these two. If you have 2 blacks, a blue, and a white, see here: http://www.dsmtuners.com/forums/attachment.php?attachmentid=48046
For 2g:
(From 99 Mitsubishi Eclipse factory manual)
Harness side: Red (power) and yellow are for the heaters (red and yellow/black for rear O2). White is signal and black is signal ground (on 2g's this is NOT the same as engine/chassis ground and must NOT be connected there). The signal and signal ground are usually shielded. The connectors are different and have different pins.
Important note: On a 2g (but not 1g) ECU pin 92 (note: this pin is incorrectly labeled Ignition switch on some 2g ECU pinout diagrams) goes to the signal grounds of the following engine sensors: manifold diff pressure, engine coolant temp, front O2, rear O2, TPS, volume air flow (MAF), and on the 98 & 99 fuel tank diff pressure. Pin 92 is grounded inside the ECU but all these sensors signal grounds must NOT be grounded anywhere but through pin 92 to avoid electrical noise and ground loops from affecting the sensors differential signals and to guarantee that the sensor's ground is at the exact same voltage potential as the ECU ground (which it might not be with large current flowing through any other ground). Some people and even some mechanics, don't know/realize this and they mistakenly connect signal ground to the engine (as in a 1g). A typical example is when replacing the front O2 sensor and the harness connector/wires are damaged and need replacing. Connecting the O2 signal ground to the engine/chassis (or even battery negative) can cause misleading and noisy signals to the ECU causing the ECU to run the engine poorly. And if it is still also connected to the original harness signal ground wire, then all of the above engine sensors will also have that problem.
Sensor side: Every aftermarket O2 has different color wires (http://www.academia.edu/5496281/O2_...from_http_www.hiflo.com.au_oxygen_sensors.cfm). The 2 same color wires, usually white (but sometimes black), are the heaters (go either polarity - they measure about 12 ohms so you can easily find them even if they are not the same color). The other 2 are the signal and signal ground wires. If one is black it's usually the signal (so the other is the signal ground). If that doesn't work reverse them.
[On my 99 Eclipse, the sensor side of the factory O2 had 2 blacks for heaters, blue for signal (went to harness side white), and white for signal ground (went to harness side black).]
For 1g:
(From DSM Backup manual for 91 DOHC turbo)
Looking from the wire side, the harness round connector has pin 1 in upper left, 2 upper right, 3 lower left, 4 lower right. This would also be the way it looks on the sensor round connector if looking at the connector with the wires on it's opposite side. (Can also see here: http://www.dsmtuners.com/forums/bolt-tech/171244-o2-sensor-wiring.html#post1431571)
Harness side: Red (pin 3 - goes to MPI relay for power) and black (pin 4 - goes to ground) are for the heaters. White (pin 1 - goes to ECU pin 4) is signal. Black (pin 2) is signal ground (goes to engine ground on a 1g). The signal and signal ground are usually shielded.
Sensor side: Every aftermarket O2 has different color wires (http://www.academia.edu/5496281/O2_...from_http_www.hiflo.com.au_oxygen_sensors.cfm). The 2 same color wires, usually white (but sometimes black), are the heaters (go either polarity - they measure about 12 ohms so you can easily find them even if they are not the same color). The other 2 are the signal and signal ground wires. If black and grey, try the sensor black to harness white and sensor grey to harness black. If it doesn't work reverse these two. If you have 2 blacks, a blue, and a white, see here: http://www.dsmtuners.com/forums/attachment.php?attachmentid=48046
For 2g:
(From 99 Mitsubishi Eclipse factory manual)
Harness side: Red (power) and yellow are for the heaters (red and yellow/black for rear O2). White is signal and black is signal ground (on 2g's this is NOT the same as engine/chassis ground and must NOT be connected there). The signal and signal ground are usually shielded. The connectors are different and have different pins.
Important note: On a 2g (but not 1g) ECU pin 92 (note: this pin is incorrectly labeled Ignition switch on some 2g ECU pinout diagrams) goes to the signal grounds of the following engine sensors: manifold diff pressure, engine coolant temp, front O2, rear O2, TPS, volume air flow (MAF), and on the 98 & 99 fuel tank diff pressure. Pin 92 is grounded inside the ECU but all these sensors signal grounds must NOT be grounded anywhere but through pin 92 to avoid electrical noise and ground loops from affecting the sensors differential signals and to guarantee that the sensor's ground is at the exact same voltage potential as the ECU ground (which it might not be with large current flowing through any other ground). Some people and even some mechanics, don't know/realize this and they mistakenly connect signal ground to the engine (as in a 1g). A typical example is when replacing the front O2 sensor and the harness connector/wires are damaged and need replacing. Connecting the O2 signal ground to the engine/chassis (or even battery negative) can cause misleading and noisy signals to the ECU causing the ECU to run the engine poorly. And if it is still also connected to the original harness signal ground wire, then all of the above engine sensors will also have that problem.
Sensor side: Every aftermarket O2 has different color wires (http://www.academia.edu/5496281/O2_...from_http_www.hiflo.com.au_oxygen_sensors.cfm). The 2 same color wires, usually white (but sometimes black), are the heaters (go either polarity - they measure about 12 ohms so you can easily find them even if they are not the same color). The other 2 are the signal and signal ground wires. If one is black it's usually the signal (so the other is the signal ground). If that doesn't work reverse them.
[On my 99 Eclipse, the sensor side of the factory O2 had 2 blacks for heaters, blue for signal (went to harness side white), and white for signal ground (went to harness side black).]
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