Fuel Pump Relay Location & Identification

1992MustangGT

Member
Sep 6, 2008
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Washington State
I have a 1992 Mustang Gt 5.0 and I’m having a problem with it shutting off when it’s running. The problem started a long time ago and was extremely random and it would just shut off for maybe 1-5 seconds and then the engine would automatically turn back on (I assume because I was driving down the road and since it’s a 5-speed, it fired back up because of the wheels turning the motor). However, the problem is getting a lot worse and a lot more frequent.

I put a scanner on it and read the codes and it came up with 3 codes: 34, 67, & 96.

34 = Insufficient EGR flow or EVP voltage hight (SONIC) or PFE sensor voltage high or out of specification.

67 = Clutch switch circuit failure / neutral drive switch (NDS) circuit failure, circuit open; or A/C input high.

96 = Fuel pump secondary circuit fault / high speed fuel pump relay open.

After doing some research on this problem, it seems that the problem might be the fuel pump relay. I wasn’t sure where the relay was located, but what I was told is that it’s either under the driver’s seat or on the passenger side fender well in front of the shock tower. Upon inspecting my car, I found two relays on the passenger side fender well in the front of the shock tower. From what I was told, one relay is for the A/C cutoff at WOT and the other is the fuel pump relay.

So I went to NAPA and bought a new fuel pump relay. When I got home and went to install it, I discovered the shape, size and pins weren’t the same as the one on my car (SEE PICTURES). All the research I’ve done shows the fuel pump relay is the same as the one I bought from Napa (on the right in the pictures). But as you can see, mine is a different size and shape and has more of a standard relay pin layout.

Is the relay I found on my car the fuel pump relay or is it something else? If it’s not, where is it located? If this is the fuel pump relay, why is it different than the one from Napa and all the other auto part stores I’ve looked at? Autozone has the same relay as Napa, which is different than mine. Not sure what to do at this point. I don’t know what relay I have or what to buy to replace it. Can anyone shed some light on this? Thanks.
Fuel Pump Relay--1.jpg
Fuel Pump Relay--2.jpg
 
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jrichker

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The relay on the left is the real fuel pump relay.
The other one is mismarked or the wrong part number.

Code 96 causes & tests 91-93 models. – KOEO- Fuel pump monitor circuit shows no power - Fuel pump relay or battery power feed was open - Power / Fuel Pump Circuits. The fuel pump circuit lost power at one time or another.

Revised 24-Mar-2017 to add text about the A/C Wide Open Throttle relay and using the wire colors to identify which relay is the fuel pump relay

Clear the codes by disconnecting the battery and turning on the headlights for about 5 minutes before reconnecting the battery. This will clear any remaining codes. Drive the car for several days and dump the codes again. In many cases, this clears the 96 code.

Look for a failing fuel pump relay, bad connections or broken wiring. On 91 model cars, the fuel pump relay is under the driver’s seat. The fuel pump relay is located under the Mass Air Meter on Fox bodied stangs built after 91. It can be confused with the A/C Wide Open Throttle relay which is in the same area. Use the wire colors as shown in the diagram below to identify which relay is the fuel pump relay.

Diagram of the fuel pump wiring for 91-93 cars.
attachment.php?attachmentid=57323&stc=1&d=1235957538.gif


Look for power at the fuel pump - the fuel pump has a connector at the rear of the car with a pink/black wire and a black wire that goes to the fuel pump. The pink/black wire should be hot when the test connector is jumpered to the test position. To trick the fuel pump into running, find the ECC test connector and jump the connector in the lower RH corner to ground. No voltage when jumpered, check the fuel pump relay and fuse links.

attachment.php?attachmentid=68357&stc=1&d=1322348015.gif



Power feed: Look for 12 volts at the pink/black wire (power source for fuel pump relay). No voltage or low voltage, bad fuse link, bad wiring, or connections. Remember that on 92 or later models the fuel pump relay is located under the Mass Air meter. Watch out for the WOT A/C control relay on these cars, as it is located in the same place and can easily be mistaken for the fuel pump relay.

Relay: Turn on the key and jumper the ECC test connector as previously described. Look for 12 volts at the dark green\yellow wire (relay controlled power for the fuel pump). No voltage there means that the relay has failed, or there is a broken wire in the relay control circuit. Be sure to closely check the condition of the relay, wiring & socket for corrosion and damage.

attachment.php?attachmentid=49675&d=1175374071.gif


91-93 Models:
Using the diagram, check the dark green/yellow wire from the fuel pump relay: you should see 12 volts or so. If not the relay has failed or is intermittent. Check the inertia switch: on a hatch it is on the drivers side by the taillight. Look for a black rubber plug that pops out: if you don't find it, then loosen up the plastic trim. Check for voltage on both sides of the switch. If there is voltage on both sides, then check the Pink/black wire on the fuel pump relay: it is the power feed to the fuel pump. Good voltage there, then the fuel pump is the likely culprit since it is getting power. No voltage there, check the Pink/black wire, it is the power feed to the fuel pump relay & has a fuse link in it. Good voltage there & at the dark green/yellow wire, swap the relay.

All testing is done with the ignition switch in the Run position. Do not forget this crucial step.

The pink/black wire s should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the fuse link for the fuel pump has opened up.

With the test jumper in place the green/yellow wire should be the same voltage as the pink/black wire +/- 0.25 volt.

If not, look at the red wire: should have the same voltage as the battery positive terminal +/- 0.25 volt.
If not, then check the yellow wire on the EEC relay located on top of the computer. This one is hard to get to. It should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the fuse link for the computer has opened up.

If the red wire does not have the same voltage as the battery positive terminal +/- 0.25 volt and the yellow wire on the EEC relay does, then check the red/green wire on the EEC relay. It should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the ignition switch is defective or the fuse link in the ignition wiring harness has opened up, or the EEC relay is defective.

All testing is done with the ignition switch in the Run position. Do not forget this crucial step.

The pink/black wire s should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the fuse link for the fuel pump has opened up.

With the test jumper in place the green/yellow wire should be the same voltage as the pink/black wire +/- 0.25 volt.

If not, look at the red wire: should have the same voltage as the battery positive terminal +/- 0.25 volt.
If not, then check the yellow wire on the EEC relay located on top of the computer. This one is hard to get to. It should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the fuse link for the computer has opened up.

If the red wire does not have the same voltage as the battery positive terminal +/- 0.25 volt and the yellow wire on the EEC relay does, then check the red/green wire on the EEC relay. It should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the ignition switch is defective or the fuse link in the ignition wiring harness has opened up, or the EEC relay is defective.

Diagram courtesy of Tmoss & Stang&2birds
IgnitionSwitchWiring.gif
 

1992MustangGT

Member
Sep 6, 2008
122
2
19
Washington State
The relay on the left is the real fuel pump relay.
The other one is mismarked or the wrong part number.

Code 96 causes & tests 91-93 models. – KOEO- Fuel pump monitor circuit shows no power - Fuel pump relay or battery power feed was open - Power / Fuel Pump Circuits. The fuel pump circuit lost power at one time or another.

Revised 24-Mar-2017 to add text about the A/C Wide Open Throttle relay and using the wire colors to identify which relay is the fuel pump relay

Clear the codes by disconnecting the battery and turning on the headlights for about 5 minutes before reconnecting the battery. This will clear any remaining codes. Drive the car for several days and dump the codes again. In many cases, this clears the 96 code.

Look for a failing fuel pump relay, bad connections or broken wiring. On 91 model cars, the fuel pump relay is under the driver’s seat. The fuel pump relay is located under the Mass Air Meter on Fox bodied stangs built after 91. It can be confused with the A/C Wide Open Throttle relay which is in the same area. Use the wire colors as shown in the diagram below to identify which relay is the fuel pump relay.

Diagram of the fuel pump wiring for 91-93 cars.
attachment.php?attachmentid=57323&stc=1&d=1235957538.gif


Look for power at the fuel pump - the fuel pump has a connector at the rear of the car with a pink/black wire and a black wire that goes to the fuel pump. The pink/black wire should be hot when the test connector is jumpered to the test position. To trick the fuel pump into running, find the ECC test connector and jump the connector in the lower RH corner to ground. No voltage when jumpered, check the fuel pump relay and fuse links.

attachment.php?attachmentid=68357&stc=1&d=1322348015.gif



Power feed: Look for 12 volts at the pink/black wire (power source for fuel pump relay). No voltage or low voltage, bad fuse link, bad wiring, or connections. Remember that on 92 or later models the fuel pump relay is located under the Mass Air meter. Watch out for the WOT A/C control relay on these cars, as it is located in the same place and can easily be mistaken for the fuel pump relay.

Relay: Turn on the key and jumper the ECC test connector as previously described. Look for 12 volts at the dark green\yellow wire (relay controlled power for the fuel pump). No voltage there means that the relay has failed, or there is a broken wire in the relay control circuit. Be sure to closely check the condition of the relay, wiring & socket for corrosion and damage.

attachment.php?attachmentid=49675&d=1175374071.gif


91-93 Models:
Using the diagram, check the dark green/yellow wire from the fuel pump relay: you should see 12 volts or so. If not the relay has failed or is intermittent. Check the inertia switch: on a hatch it is on the drivers side by the taillight. Look for a black rubber plug that pops out: if you don't find it, then loosen up the plastic trim. Check for voltage on both sides of the switch. If there is voltage on both sides, then check the Pink/black wire on the fuel pump relay: it is the power feed to the fuel pump. Good voltage there, then the fuel pump is the likely culprit since it is getting power. No voltage there, check the Pink/black wire, it is the power feed to the fuel pump relay & has a fuse link in it. Good voltage there & at the dark green/yellow wire, swap the relay.

All testing is done with the ignition switch in the Run position. Do not forget this crucial step.

The pink/black wire s should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the fuse link for the fuel pump has opened up.

With the test jumper in place the green/yellow wire should be the same voltage as the pink/black wire +/- 0.25 volt.

If not, look at the red wire: should have the same voltage as the battery positive terminal +/- 0.25 volt.
If not, then check the yellow wire on the EEC relay located on top of the computer. This one is hard to get to. It should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the fuse link for the computer has opened up.

If the red wire does not have the same voltage as the battery positive terminal +/- 0.25 volt and the yellow wire on the EEC relay does, then check the red/green wire on the EEC relay. It should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the ignition switch is defective or the fuse link in the ignition wiring harness has opened up, or the EEC relay is defective.

All testing is done with the ignition switch in the Run position. Do not forget this crucial step.

The pink/black wire s should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the fuse link for the fuel pump has opened up.

With the test jumper in place the green/yellow wire should be the same voltage as the pink/black wire +/- 0.25 volt.

If not, look at the red wire: should have the same voltage as the battery positive terminal +/- 0.25 volt.
If not, then check the yellow wire on the EEC relay located on top of the computer. This one is hard to get to. It should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the fuse link for the computer has opened up.

If the red wire does not have the same voltage as the battery positive terminal +/- 0.25 volt and the yellow wire on the EEC relay does, then check the red/green wire on the EEC relay. It should have the same voltage as the battery positive terminal +/- 0.25 volt. If not, then the ignition switch is defective or the fuse link in the ignition wiring harness has opened up, or the EEC relay is defective.

Diagram courtesy of Tmoss & Stang&2birds
IgnitionSwitchWiring.gif
Thank you for that excellent reply and description. I will definitely do some testing as you outlined. I will attempt to do that this weekend.

Let me add something to this scenario that I just remembered. There was one incident when I was driving down the highway and I had the radio on and all of a sudden the radio shut off for about 3-5 seconds and then came back on. Then about 30 seconds later, the car shut off and came back on. So if the radio is shutting off, but the car is still running do you think the fuel pump relay is the issue??? Given the trouble codes that showed up (that I posted in my original post), what do you guys thing is causing my problem with the car shutting off? Does this point more towards an ignition switch issue or ????
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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It could be, or not, you are going to get at least a half dozen 'maybe this or that' answers. Start with the tests outlined by jrichker in post two and we can help from there.
One of the most important and often overlooked things are connections, on these efi cars the grounds are often at fault so check your grounds and do the testing before randomly replacing stuff that someone thinks might be the problem.
 

1992MustangGT

Member
Sep 6, 2008
122
2
19
Washington State
It could be, or not, you are going to get at least a half dozen 'maybe this or that' answers. Start with the tests outlined by jrichker in post two and we can help from there.
One of the most important and often overlooked things are connections, on these efi cars the grounds are often at fault so check your grounds and do the testing before randomly replacing stuff that someone thinks might be the problem.
I'll definitely do some electrical testing following the instructions and diagrams jrichker provided. I just felt it was important to provide the radio cutting out info to help diagnose a possible problem. I might have more than one problem and don't realize it. Who knows. I appreciate your input and will work on it this weekend if the rain stops.
 

jrichker

StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
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Dublin GA
The ignition switch is a known problem with Fox body Mustangs. I would recommend replacing it as preventive maintenance .

Recall on Ford Ignition switches:

Revised 7-June-2014 to add Torx bit picture and source. Also added replacement ignition switch wiring pigtail picture, part numbers and sources.

Some of the symptoms of ignition switch problems are things that don’t work or are intermittent like radio, turn signals, wipers or heater.

There was a FREE recall on Ford ignition switches. They overheat and sometimes catch fire. That burns up the steering column and sometimes the car interior. Since this is very old information, you may not be able to get the switch replaced for free anymore. The auto parts stores sell the switches for $13-$15.

4.jpg


4.jpg


4.jpg


While you are working on the switch, check the wiring and connector closely. A replacement connector with new wiring pigtails is available from most auto parts stores

AutoZone and Advanced Auto Parts have the same Part Number: 434 - may have to order, not always in stock

Advanced Auto Parts alternate part number: PT5534

20974527_bwd_pt5534_pri_larg.jpg


Saleen0679 was nice enough to dig this up for us awhile back: Replace a 1979-1993 Ignition Switch Assembly

Torx bit set from Advance Auto Parts



Autocraft torx bit set – have small hole in tip for tamper proof screws.
Part No. AC571/W1386 Cost approx. $12 +tax

Diagrams courtesy of Tmoss & Stang&2birds

Ignition switch wiring


Fuel, alternator, A/C and ignition wiring


See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/ Everyone should bookmark this site.

Complete computer, actuator & sensor wiring diagram for 91-93 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/91-93_5.0_EEC_Wiring_Diagram.gif

Complete computer, actuator & sensor wiring diagram for 88-91 Mass Air Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Ignition switch wiring
http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

Fuel, alternator, A/C and ignition wiring
http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

O2 sensor wiring harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangO2Harness.gif

Vacuum diagram 89-93 Mustangs
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxFordVacuumDiagram.jpg

HVAC vacuum diagram
http://www.veryuseful.com/mustang/tech/engine/images/Mustang_AC_heat_vacuum_controls.gif

TFI module differences & pin out
http://www.veryuseful.com/mustang/tech/engine/images/TFI_5.0_comparison.gif

Fuse box layout
http://www.veryuseful.com/mustang/tech/engine/images/MustangFuseBox.gif

87-92 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang87-92 PowerWindowWiring.gif

93 power window wiring
http://www.veryuseful.com/mustang/tech/engine/images/mustang93PowerWindows.gif

Visual comparison of the Ford Fuel Injectors, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/Ford_Injector_Guide.jpg
 

1992MustangGT

Member
Sep 6, 2008
122
2
19
Washington State
Jrichker, you are the freaking man!!!! Thank you so much for all that detailed information and all the links you provided. You have gone above and beyond and you have no idea how much I appreciate it!!!

After reading the info you provided about the ignition switches being a hazard, I just might replace it regardless if the case is separating or not. The car is 25 years old and I would feel much better knowing it's been replaced.

A few years ago I stumbled across an article regarding problems with the wiring that controls both the headlights and fog lights; both were on the same circuit and the wiring isn't a thick enough gauge to handle the load and it ends up burning up and sometimes catching fire. Well I experienced this exact problem first hand, but thankfully it didn't get to the point of catching fire yet. I was driving at night with the fog lights on and all of a sudden my headlights went out. Thank the Lord the driving lights were still on and gave me enough light to somewhat see the lines on the road so I didn't end up in a ditch. After messing with the switch (turning it off and on and wiggling it; not sure if it helped or not), the lights came back on. But then they went off again. This happened a few different times so I researched and found the article I had read a few years before and rewired the headlights separate from the fog lights and put the fog lights on a relay. Upon doing this I noticed the wiring plug was burned and melted a little bit, so it was getting really hot running both the headlights and fog lights at the same time. Thankfully it didn't burn the car to the ground. But ever since I put the fog lights on it's own circuit, I haven't had a problem. And the cool thing is now I can turn on the fog lights without having to turn on the headlights, which is not an option the way Ford had it wired.

I guess my point is, I believe you about the ignition switch being a fire hazard due to the issues I've had with the headlights and because of that I'm going to replace the switch as a preventative safety measure. And who knows, I may get lucky and it solves my problem I'm currently having. Thanks again for all the help. I'll let you know how it turns out.
 

1992MustangGT

Member
Sep 6, 2008
122
2
19
Washington State
Well, I do believe I found out why my Mustang has been shutting off. I bought a new ignition switch and now I need to buy a new connector. I'm thankful this isn't a very expensive or difficult fix. I'm even more thankful that I caught it before my car went up in flames.
 

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jrichker

StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
27,134
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Dublin GA
I'm glad to be of help.

It is good to know that you found and fixed it before it did any more damage.