Electrical Main Engine Harness (how To Id Year)

[fredfifty]

Does it matter which O2 manual harness i have with an A9L ecm? I know there are 88-90 and 91-93 harnesses. My car originally had a 88-90 manual O2 harness when i had an A9P ecm. Now, i have an A9L with a 91-93 manual O2 harness, but my car runs rich and white smoke comes out the driver side tailpipe only. Should i switch the harness back to the 88-90 one? Im thinking my car might have the main engine harness for an 88-90 put in by the previous owner, whom i cannot contact anymore. Is there a way to tell what year engine harness i have by markings or identifiers? That is, if the main engine harness year makes a difference.

 

[General karthief]

There is usually a tag near the ecm on the harness but after so many years they can fall off or are unreadable, there may be tags on other parts of the harness, there may be a way by wire position or colors, check veryuseful.com for wire diagrams

 

[Mustang5L5]

The jumper colors are different. Earlier harnesses had a purple jumper. Later models used a green jumper.

Wire colors remained the same during the years. The o2 harness wire locations for the sensors themselves may have moved. Look at your harness on both sides and see what colors go to what colors on the opposite side. I want to say the O2 sensor wires did go to different spots on the harness.

I would have left the early harness in place and just move the jumper wire. Just use a small pick to pull the red plastic insert out of the connector, and then move the wire to the correct spot. You might need to drill a small hole in the rubber on the backside before inserting the pin. Then lock it down with the red clip.

Before you start the car, remove the ECU and insert a probe from a Multimeter on pin 46 to ground. Crank the engine (wont stard with no ECU) and see if you have any voltage on pin 46. If you do, the ECU will fry. You want 0 volts on pin 46.

 

[Mustang5L5]

I believe this is the wiring for the earlier auto and manual harness up to 1991

Connector 40 should be the pin locations for the various wires. Match them to the colors in the first pic on both sides of the harness and see if they make sense

For instance, white/pink wire is for the low oil sensor. This should be the same colors on both sides of the harness. Both O2 sensors share a Gray/Yellow and Black/Green wire, but the 3rd wire is different. Blue/yellow is left, red/blk is right side.

 

[Mustang5L5]

One more photo. O2 sensor wire colors stayed the same year for year. So the colors here should be correct. Low oil wire is #258 in the diagram