O2 Harness Differences. Jumper Wire. Does It Matter For A Sd Harness?

JohnnyK81

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Sep 17, 2007
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So I had installed a 1988ish 5.0 in my 1967 a few years ago, and then added MAF, and switched the computer to an A9l.

I had also moved the MAF and O2 power to all run off a relay to lighten the electrical load.

Then only recently, it was brought to my attention that there is a jumper difference between harnesses that can burn out the computer, make it run poorly, etc. I took my harness apart, and noticed I didn't have a jumper!

I forgot I think I used a 1988 harness. So there is no jumper. Is there anything specific I would have to do in this case? Or should everything be running great (it's not, but that could be a multitude of many other things). Jumper wire + computer selection only applies to 1989+ that came with MAF? I'm in the clear?

If not, please enlighten me!

Thanks guys. Pic included of the back of my plug. The white/pink wire is snipped off. IIRC, that is low oil sensor on the original fox pan?
 
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Mustang5L5

This is a big reason why I pulled it out
Mod Dude
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I think transmission is more critical than SD or MAF.

From what i've read, PIN 46 is the culprit. You want 0 voltage on this particular pin otherwise you'll short out the ECM. Swapping the harnesses can sometimes power up this pin?

How to check? I beleive you want to remove the EEC, and put a test lead on pin 46 to ground and then test in various key on, key off, key cranking, ACC positions.

Google "Mustang Pin 46" for more info
 

JohnnyK81

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Sep 17, 2007
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Oh man, so confused. :D Thanks for the reply. So this applies even though I started with an SD harness, and then added MAF?

What do you mean by transmission is more critical?

Thanks!
 

Mustang5L5

This is a big reason why I pulled it out
Mod Dude
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The two harnesses are pinned different depending on the original tranmission the Mustang. Either 5-spd or Auto. The nuetral circuit is actually routed through the harness differently. I beleive there are 4 harnesses, 87-89 and 90-93 and 1 for each trans. Nothing of the MAF runs through the harness, so regardless of how you converted the car to MAF, it shouldn't matter.

What matters is the EEC matching the harness. Soif you have an A9L, do you have a 5-spd 87-89 harness?
 

JohnnyK81

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Sep 17, 2007
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I pulled it all out of a donar car that a 5 spd.. but if it came with a 5 spd originally, I have no idea.. but the computer wasn't an a9l to begin with obviously.

But what I can't tell is there seems to be no pictures of the difference for 87 SD harnesses.. Just pictures of the later years with the jumper wire.. and the SD harness doesn't seem to have the jumper wire?
 

Mustang5L5

This is a big reason why I pulled it out
Mod Dude
Feb 18, 2001
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Mine does

1988 Automatic harness
pic.php?u=11130S5RAi&i=1147305


None of the MAF wiring runs through the O2 harness which is the harness at hand. The only difference in the 1989 MAF harness would be the addition of 7 additional wires elsewhere in the harness

Do you have a pic of your harness?
 

JohnnyK81

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Sep 17, 2007
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Hey, sorry for the late reply! I don't see the picture you posted, just "Image Not Available".

Here is the back of the harness that I believe should have the jumper.

Disregard the snipped white/pink wire. Should just be the low oil switch I believe?
IMG232 (Large).jpg
 

Mustang5L5

This is a big reason why I pulled it out
Mod Dude
Feb 18, 2001
31,749
7,945
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Ill need to dig my wiring diagrams out and check. Too late for that tonight


Sent from my iPhone 4S using Tapatalk
 

JohnnyK81

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Sep 17, 2007
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Sure, no problem. Twould be appreciated. I was looking through "Veryuseful.com" but it's not very helpful for such specifics, and I of course only have 67 manuals.

I'm just starting to wonder if, if i'm using a 1987 harness (I may be?), if anything has to be done like it does for the 88-89+ ones with the jumper.

Thanks!