Electrical 93 LX Fuel Pump Issues w Relay & Fuse Link

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Mustang5L5

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Mod Dude
Feb 18, 2001
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I will pull it apart and get back with you later today. I also will review the others posts and wiring. I might end up re-wiring the car at this point!

I wonder if just getting the correct 1993 engine harness with the FP relay in the bay would solve all your problems.


My assumption is this. For some reason the previous owner removed the original engine harness and installed a 1991 engine harness with a 88-90 O2 sensor harness. That may have toasted the ECU. The tried to rig the fuel pump with the jumper wire because whatever they did with the underseat wiring did not work. Who knows where it runs off to.

Sound right?
 

diesel farmer

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Nov 11, 2021
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I wonder if just getting the correct 1993 engine harness with the FP relay in the bay would solve all your problems.


My assumption is this. For some reason the previous owner removed the original engine harness and installed a 1991 engine harness with a 88-90 O2 sensor harness. That may have toasted the ECU. The tried to rig the fuel pump with the jumper wire because whatever they did with the underseat wiring did not work. Who knows where it runs off to.

Sound right?
I think your observations are correct based on what we have found thus far. For what it's worth, I think the engine has been out of the car and maybe it's a different year engine too -- maybe I'll pull the engine starter and see if I can get numbers off the block to determine what year block it is. Although I don't think it matters what year engine is in the car, does it?

Before I try to find a correct 93 harness, let me do a little more digging.
 

diesel farmer

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Nov 11, 2021
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I think those 8 wires are C230 and C297 courtesy door light switch.

Reason I say that is because the main harness running to the rear of the car has 5 plugs according to the diagram. Two are the 12-pin, one is the round 8-pin.

The trans 8-pin black is a separate harness.


Is the door switch hooked up? Or os that cut too? What about the power Windows/doors? Those functional?


I need to look at the diagram in a bit. What about the pass side? Anything disconnected or cut there?

Power windows on both sides do work. Door switches do not work. Power mirrors do not work. I have not tried to figure out the door switches or mirrors.

I haven't seen any other wires cut or disconnected other than the air bag sensors which were not connected.
 

diesel farmer

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Nov 11, 2021
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C297 LH courtesey light looks to have 4 wires.

black/light blue
Red/pink
And two light green/yellow
I don't that this car has any courtesy lights that work. It's got a factory sun roof and the wire is still up in the front center of the roof where the chrome light is normally located, but it's missing. I don't see that color combination of wires in the left kick panel.
 

Mustang5L5

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Mod Dude
Feb 18, 2001
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Courtesey lights are probably low priority.

Here’s the drivers side power mirror. You are missing C230 which is a 4-pin plug but only has three wires

Red
Yellow
Dark blue

It’s possible 2 yellows connect here, as the 2nd yellow would be the ground for the other side.

2B10515F-4180-4FD4-B45D-EC1D7CB25E91.jpeg
 

diesel farmer

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Nov 11, 2021
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Where does your fuel pump relay under the seat tie into the main harness? Are you able to trace that back to a connector?

The wires from the fuel pump relay go back over to the kick panel side - I think the green-yellow one is in this pigtail, the second wire from the lower right - but notice again how the wires don't match up (color wise) on the engine side vs. the inside-of-car side of the harness? I think this helps to prove there are two different years of harness: year 93 on the inside and likely 91 in the engine bay. Wow, it took quite a time to figure that out!

It might be best to track down the correct 93 engine harness as you suggested. Do I try to find a used harness online or try an aftermarket harness option?
 

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Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
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You might be able to make that work. All depends on how much time you want to spend on it. This is the gray 12-pin connector? C207

Cheapest 1993 harness i see on Ebay right now is just under $400.


Otherwise you can try and chase the wire colors through the 91 and 93 harnesses to see what wire should match up to what.
 

diesel farmer

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Nov 11, 2021
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Thanks. I think I'm going to pull the engine harness from the car and see if I can figure out what is going on -- I will have to pull it anyway if I get a different 93 harness to install.

I am still puzzled by the fact that we think the interior harness is from a 93 given the door switch wiring, but if that is the case, then why is the fuel pump relay (which is part of the interior harness) under the seat in this car when it should be in the engine bay?! I wonder if someone in the past re-wired part of the interior harness.
 

diesel farmer

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Nov 11, 2021
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I have been studying wire diagrams this evening. Let's note that wiring is not my specialty. :( Are the below two statements correct?

1. The wires coming into the pigtail (see pic 32) should be the same color on both sides of it -- or did Ford change wire colors coming in/out of a pigtail/connector?

2. There should be a blue-orange wire located in the second position to the left in pic 25 which feeds (or comes from ECU pin 22 to) the blue-orange wire located in the second position from the left (in pic 24) that goes to the fuel pump relay.
 

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Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
39,486
15,332
224
I am still puzzled by the fact that we think the interior harness is from a 93 given the door switch wiring, but if that is the case, then why is the fuel pump relay (which is part of the interior harness) under the seat in this car when it should be in the engine bay?! I wonder if someone in the past re-wired part of the interior harness.

The dash harness is def 1993 given that you found an F3 tag on it near the booster. That’s a 1993 part number. Also, integrated door/window switches is a 92-93 only thing.


Now, the harness that the fuel pump relay plugs into might be from an earlier car. That still needs to be confirmed
 
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diesel farmer

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Nov 11, 2021
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I have my hands on a year 93 EVTM. In the EVTM...
-- where does the EVTM tell the pin size (or # of pins) of e.g., connector C103 (the fuel pump relay).
-- what is the reference e.g., 151- 5- B10 used for (there is a 151- reference beside each part in the EVTM diagrams)? Does it identify the wires going into or out of a certain connector?