1988 f-150 302, auto

Went to test my codes, looks pretty straight forward -ground the self test in connector...

Well - I didn't see this one coming...

I found the triangular connector plugged into its little holder on the driver's side fender wall - and right aside of it was a small light gray connector which looked exactly like what I expected to find as the self-test-input connector.

Problem is - even though the connector is there - there's no wire in it - not even the metal contacts. It's just the shell of the connector.

... I searched for the missing wire, thinking it somehow got torn out - but it's nowhere to be found.

I opened up the wire group to that main test plug to see if maybe the wire was cut out of there - no luck.

Am I missing something? IS there supposed to be a STI plug on this truck??? I see it in the wiring schematic in the chilton manual...

Assuming there IS supposed to be a wire in my connector, am I correct in assuming this little gray connector IS is the right one? Or is it hidden away somewhere else?

Could anybody possibly tell me an eay way to locate the missing wire?

Is it supposed to be bundled in with the wires of the other test connector?

If you have a similar truck, where does the wire break out from?

 

Yes the little grey connector is the STI plug and the wire for it has to be there somewhere. That wire goes straight back to the EEC on pin 48 so worst case disconnect the EEC connector, locate the pin and hopefully there is a wire attached that you can trace back the other way. Disconnect the battery before disconecting the EEC however.

 

I've looked very thoroughly - the wire is simply not there.

I've dug into all the sections of the wiring harnesses in that area - no cut lines.

I figured maybe it was accidentally "re-purposed" by the previous owner, but I can't find any wires that are white with red (as the wiring schematic tells me it should be).

So typical - The simplest little task turns into the biggest headache.

I tried finding the control unit itself to follow it back from there - but I can't tell what I'm looking at. I'm not as flexible as I once was - and getting under the dash is a pain. The chilton manual is useless in guiding me on this.

Is it the box that's gold anodized??? under the dash - a little to the right of the accelerator pedal?

I can probably tell by the pins by pulling the connector - but I'm hesitant to yank anything under there yet for fear of breaking a connector - or worse. I have horrible luck like that.

 

No that is not the computer. The computer should be in the drivers kick panel.

And should look like this:


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The STI wire comes out of the same wiring harness that the Self-Test plug does.
See diagram below.



/

 

Wow - that's really weird. I've got that section peeled all the way to where it joins the main bunch - guess I'll just have to go further with it.

Thank you very much for that info - at least now I KNOW I'm looking in the right area - that helps considerably.

 

Did you see the diagram I posted with the wiring?

 

yes - that's what I was referring to -

It helps confirm that I'm looking in the right spot - and that it's not me - the wire is in fact just missing...

Very odd.

I'll keep digging deeper - bound to find a cut end sooner or later.

 

I KINDA wonder if this situation is rare or not. I've tried finding the STI connector on my folks '88 T-bird to no avail, and it's a one-owner car. It's just not in the wiring harness...at least, not forward of the firewall, anyway. As Conanski said, it's just a matter of putting a new wire in the EEC connector.

As the 'bird doesn't run so bad, I'm not in a hurry to install that wire...\

Pat

 

Ok - thank you to whoever told me the ecc is behind the kick panel - all makes sense now.

Found it - and that the connector to it is in the engine compartment.

That's the good news.

The bad news is that I found the wire to connector #48 is with with black

(as opposed to what's listed in the chilton manual as white with red - which I find odd because it's right next to another connector in the schematic labled white with red... not that it's a good idea to question the manual - but ... whatever)

I followed the white with black #48 wire - and it ends up in the main test connector. With the "pointy" sid of the "triangle" facing down - looking at the face of the connector - it's the one on the right. (next to the signal return pin).

For the hell of it (and reluctantly) - I grounded the white with black and nothing happened.

No codes.

- now I'm not sure I even HAVE a check engine light. It's dark and hard to see. Nothing lights up when I turn the key.

Should a check engine light blink when I turn the key to the run position?

 

Yes the CEL should come on when you turn on the key.
The black with a white stripe wire is a ground wire but I do not see a white with a black wire near your Computer plug.
The wires you should have in the self-test plug are in the diagrams below.
You should have three wires to the self-test plug and a one wire STI.

STI W/R wire #100 computer pin #48.

Self-test plug:
SIG RTN BK/W wire #359 computer pin #46.
CEL PK/LG wire #658 computer pin #17.
Fuel Pump T/LG wire #97 computer pin #22.

Wires 658 & 100:


Wire #97:


Wire #359:

/

 

Ok - no check engine light comes on when I turn the key. All I see is "rear anti lock" and the "battery"

So that perhaps explains why I'm not seeing codes there when grounding pin 48.

BUT -

My self test plug has 5 wires running to it - two of those wires (pink/lt green) going to one terminal - so really just 4 wires total depending on how you look at it.

SIG RTN BK/W wire #359 computer pin #46. CHECK
CEL PK/LG wire #658 computer pin #17. CHECK (double wires)
Fuel Pump T/LG wire #97 computer pin #22. CHECK

But then I have the white with black coming from pin 48 to the test other test terminal as stated before.

I'm going to try doing the code test with a voltmeter to see if that works, assuming my white/blk wire is really the missing white/red...

Perhaps somebody replaced the wiring harness from a different year/model??? It LOOKS original, but who knows.

 

The STI wire in the 90s changed the wire color on pin 48 to a White wire with a Purple stripe.

Make sure you do not ground the CEL PK/LG wire #658 computer pin #17 or you will burn up the output circuit in the computer for that wire.

 

Alright - I jumpered everything to test with a voltmeter (actually used a test light) - and I got codes!

My white with black wire that runs to the main test connector is in fact the input wire that's supposed to go to the stand alone connector (and is supposed to be white with red)

WHATEVER - alls well that ends well.

I got the following codes: 21, 24, 52

I'm assuming the previous owner cut the wires to the dash in order to pass inspection (not sure about other states, but in MA you fail if your check engine light is on) - but I'll get up there later to check that out. At least now I can get some info out of this thing.

Thanks again to everybody for your help!

 

I looked again. Looks white with black to me - but if somebody insisted it was white with purple, I wouldn't argue with them. Could very well be - my eyes aren't the best.