Electrical 93 LX Fuel Pump Issues w Relay & Fuse Link

Mustang5L5 · Nov 28, 2021

And 1991. C203 is in the same place, but this time C216 is next to the ECU. Also, the inertia switch is wired on the relay in 1990 &older. In 1991, the inertia switch is directly wired in line with the fuel pump power feed.

Mustang5L5 · Nov 28, 2021

And here’s 1993 which according to this is wired different. C103 is the relay in the engine bay. But these colors are different as well.

diesel farmer · Nov 28, 2021

The wiring diagrams are helpful - thank you! Here is what I have found so far in my amateur study this afternoon. The harness coming from the ECU in my 93 Mustang has wires that do NOT match the harness from the pigtail under the driver dash running to the fuel pump relay on down to the interia switch. I can tell by looking at the engine harness where it connects at the driver left side that the age of the harnesses are different.

In the below pics, see the blue-orange wire (second from lower left) running from the fuel pump relay (which is suppose to be ground to the ECU I think) is running to the pigtail connector on the left lower dash area -- and then on the opposite side of the pigtail (which comes from the ECU) there is no wire at all in that terminal position which would explain why the fuel pump relay isn't getting grounded out properly. I also can't find (or haven't yet located) any blue-orange wire coming out of the harness at the ECU location.

What doesn't make sense is that my engine harness has the brown connector at the power booster which is supposed to be on a 91 harness and when I compare it to the harness in the neomustang video, by all accounts it appears to be a 91 harness. I will do some more poking around this evening.

Mustang5L5 · Nov 28, 2021

Is that brown connector connected to anything? Are they any orphan plugs in that area? Can you take some pics?

diesel farmer · Nov 28, 2021

Here is a picture showing all four connectors on the driver floor side. The large black colored plug to the left has the blue-orange wire from the fuel pump relay.

Notice how dirty looking the wires/tape are on the engine side of the harness and how much cleaner the wire tape is on the passenger side - this leads me to believe there is a different harness coming from the engine into the driver side.

There are no orphan plugs that I can see -- but see the wires to far lower left that have been cut (like 4 red wires, 3 yellow and a blue) and I'm not sure where they ran to. I can take more pics, let me know what you'd like.

diesel farmer · Nov 28, 2021

Here is the brown connector at the booster.

diesel farmer · Nov 29, 2021

I might have a lead on a 91 wiring harness (which is out of a 91 mustang LX hatch I think) that I can get ahold of to compare the wiring to. It might be a week or two before I can get it. My Ford service manual doesn't seem to have detailed wiring diagrams.

Mustang5L5 -- What manual are you referencing to obtain the very good wiring pics that you have been posting? thanks!

Mustang5L5 · Nov 29, 2021

diesel farmer said:
Mustang5L5 -- What manual are you referencing to obtain the very good wiring pics that you have been posting? thanks!

Factory Electrical and Vacuum Troubleshooting Manuals (EVTM). You can find them on eBay and sometimes on rockauto.

I have 86-93

Mustang5L5 · Nov 29, 2021

diesel farmer said:
Here is a picture showing all four connectors on the driver floor side. The large black colored plug to the left has the blue-orange wire from the fuel pump relay.

Notice how dirty looking the wires/tape are on the engine side of the harness and how much cleaner the wire tape is on the passenger side - this leads me to believe there is a different harness coming from the engine into the driver side.

There are no orphan plugs that I can see -- but see the wires to far lower left that have been cut (like 4 red wires, 3 yellow and a blue) and I'm not sure where they ran to. I can take more pics, let me know what you'd like.

That cut harness might be critical.

Do all the plugs you have match up with this? Looks like 6 major plugs plus the 2-pin speaker plug

diesel farmer · Nov 29, 2021

Not knowing how many wires are in each plug, it can't tell definitively since I have a couple of smaller plugs that don't look quite like the photo. Can you tell roughly how many wires each pigtail/plug should have in the driver kick panel area?

Mustang5L5 · Nov 29, 2021

The EVTM tells you the size of the connector. 8-pin, 6-pin, etc. It won't tell you the the number of wires because it changes

For example a dash harness might have 8 wires, but the engine harness of the 2.3L connecting to it might have 6 wires, while a V8 might have 7. So it gets muddy.

Let me see what info i can tell you later.

Are we still assuming the body harnesses are 1991 as well, or do you want 1993?

diesel farmer · Nov 29, 2021

That makes sense on the connector size and wiring. I am pretty sure the body harness is 91 since it appears to match the neomustang description for a 91 in his youtube video. With my poor eye site it appears there are the following connectors coming off (what I refer to as) the engine harness that runs through the firewall into the driver side floor/kick panel:

- 8 pin black color
- 8 pin grey color
- 12 pin grey color
- 12 pin black color
- 3 pin grey color
- 2 pin grey color (I think speaker wire)

Mustang5L5 · Nov 29, 2021

Do you see this tag here? Can you get a part number off that?

F1? F2? something like that. Look around on other harnesses for similar part numbers. The first 2 digits will give a clue as to the engineering year. F2 for instance would be 1992 (or later). E = 198x. F = 199x

diesel farmer · Nov 29, 2021

F3ZB

Mustang5L5 · Nov 29, 2021

That would be a 1993 harness there.

That’s the dash harness. The actual engine eec harness poles through the firewall on the pass side. See if there’s a label over there.

Mustang5L5 · Nov 29, 2021

One other thing to check.

Pull out pne of the window switches.

87-91 have connections at the switch where they can be removed, like this.

92-93 it’s part of the harness

If it’s the latter then that helps confirm your interior harnesses are 1993.

As for the engine harness, we are assuming it’s 1991 due to the lack of fuel pump relay, but I wonder if we should shelve that assumption. Look over that harness fpr a label. I agreee that it looks like the harness is from a different car based on the filth on it.

I’ll look up those connections in a bit based on a 1993 as that part number confirms a 93 dash harness and the door locks will seal the deal that the wiring inside is all original.

As to how the fuel pump is wired, I think the cut wires have something to do with that

Mustang5L5 · Nov 29, 2021

1993 EVTM

C203 Black 12-pin
C204 gray 2-pin
C207 gray 12-pin
C212 black 8-pin (this is the transmission harness)
C217 gray 8-pin (round)
C221 gray 8-pin
C224 blue 6-pin (converible onlu so may not be there at all)
C227. Gray 2-pin (door speaker)
C230 black 4-pin
C2104 gray 5-pin (convertible only so may not be there)

diesel farmer · Nov 29, 2021

Mustang5L5 said:
One other thing to check.

Pull out pne of the window switches.

87-91 have connections at the switch where they can be removed, like this.

92-93 it’s part of the harness

If it’s the latter then that helps confirm your interior harnesses are 1993.

As for the engine harness, we are assuming it’s 1991 due to the lack of fuel pump relay, but I wonder if we should shelve that assumption. Look over that harness fpr a label. I agreee that it looks like the harness is from a different car based on the filth on it.

I’ll look up those connections in a bit based on a 1993 as that part number confirms a 93 dash harness and the door locks will seal the deal that the wiring inside is all original.

As to how the fuel pump is wired, I think the cut wires have something to do with that

I don't see any other labels/tags on the engine harness.

Looks like I have the one piece harness -- here is a pic of the driver side door window switch.

diesel farmer · Nov 29, 2021

Mustang5L5 said:
1993 EVTM

C203 Black 12-pin
C204 gray 2-pin
C207 gray 12-pin
C212 black 8-pin (this is the transmission harness)
C217 gray 8-pin (round)
C221 gray 8-pin
C224 blue 6-pin (converible onlu so may not be there at all)
C227. Gray 2-pin (door speaker)
C230 black 4-pin
C2104 gray 5-pin (convertible only so may not be there)

I don't have a convertible - it's a hatch. It looks like I have most of those gray/black connectors, but it looks like this diagram has one or two extra connectors, but it's difficult to tell for sure without pulling the fuse panel and harness out.

Here is a pic of the wires that are cut off which you have been curious about -- they appear to be coming from or going to the harness which goes under the driver side floor bay to the rear of the car.

Mustang5L5 · Nov 29, 2021

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?

Electrical 93 LX Fuel Pump Issues w Relay & Fuse Link

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