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1989 Mustang 5.0 GT O2 sensor wiring harness help needed

10637 Views 4 Replies 3 Participants Last post by  Marunos
We've picked up a 1989 Mustang with a 5.0L engine and 5-speed transmission. Unfortunately, there's no wiring harness from the oxygen sensors into the main harness. We need the 8-pin connector schematic for how it connects into the main harness.

We've been scouring forums and all we've been able to find is the EEC pin-out diagram.

Does anyone have the schematic or know where we can find one? Maybe someone has a picture of the connector showing the wiring configuration?

Any help is GREATLY appreciated!
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Mustang FAQ - Wiring, Engine, Air Bag, ABS Home Page has the diagram you are looking for.

Welcome to the forum! :)
Thanks for the info!

I can see the wire colors used in the Mustang Main Harness for connector #40 as shown here. I also see connector #42 shown here in the HEGO O2 harness. The colors

Maybe this is a stupid question but how do I know which color goes to which pin in the connector as it plugs into the main harness? I guess I'm thinking that I need to pull back the casing on the main harness to see what color wires on that side and then match up the wires so that when the male/female ends are plugged in that they line up?
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I am pretty sure you'll find a pin-out for the HEGO harness at that link I gave, and be able to match up wire colors with the main harness plug.

The easiest way is to just buy a new HEGO harness. Then you don't have to think at all. :) Just plug and go. You can get one cheap at a U-Pull-It yard.
PLEASE PLEASE PLEASE make sure that your pins from your main harness are in match with pins from O2 sensors harness. If you fail to do so , your computer will be toast right with car start.
Read this thread:
RPM Rising to 3K after Installing New O2 Sensors!!! Please Help - Mustang Forums at StangNet
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