blue/orange fuse link for fuel pump

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jrichker

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See the following website for some help from Tmoss (diagram designer) & Stang&2Birds
(website host) for help on 86-95 5.0 Mustang wiring Mustang FAQ - Engine Information Everyone should bookmark this site.


Diagrams courtesy of Tmoss & Stang&2birds


http://www.veryuseful.com/mustang/tech/engine/images/88-91eecPinout.gif

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



Fuel Pump Troubleshooting for 87-90 Mustangs

Clue – listen for the fuel pump to prime when you first turn the ignition switch on.
It should run for 2-5 seconds and shut off. This on and off again cycle helps to prevent
flooding the engine when cranking. To trick the fuel pump into running, find the ECC
test connector and jump the connector in the upper RH corner to ground.






If the fuse links are OK, you will have power to the pump. Check fuel pressure –
remove the cap from the Schrader valve behind the alternator and depress the
core. Fuel should squirt out, catch it in a rag. A tire pressure gauge can also be
used if you have one - look for 37-40 PSI. Beware of fire hazard when you do this.

No fuel pressure, possible failed items in order of their probability:
A.) Tripped inertia switch – press reset button on the inertia switch. The hatch
cars hide it under the plastic trim covering the driver's side taillight. Use the
voltmeter or test light to make sure you have power to both sides of the switch

B.) Fuel pump power relay – located under the driver’s seat in most stangs built
before 92.
C.) Clogged fuel filter
D.) Failed fuel pump
E.) Blown fuse link in wiring harness.
F.) Fuel pressure regulator failed. Remove vacuum line from regulator and inspect
for fuel escaping while pump is running.

The electrical circuit for the fuel pump has two paths, a control path and a power
path.

The control path consists of the inertia switch, the computer, and the fuel pump
relay coil. It turns the fuel pump relay on or off under computer control. The
switched power (red wire) from the ECC relay goes to the inertia switch
(red/black wire) then from the inertia switch to the relay coil and then from the
relay coil to the computer (tan/ Lt green wire). The computer provides the ground
path to complete the circuit. This ground causes the relay coil to energize and
close the contacts for the power path. Keep in mind that you can have voltage
to all the right places, but the computer must provide a ground. If there is no
ground, the relay will not close the power contacts.

The power path picks up from a fuse link near the starter relay. Fuse links are like
fuses, except they are pieces of wire and are made right into the wiring harness.
The feed wire from the fuse link (orange/ light blue wire) goes to the fuel pump
relay contacts. When the contacts close because the relay energizes, the power
flows through the contacts to the fuel pump (light pink/black wire). Notice that
pin 19 on the computer is the monitor to make sure the pump has power.
The fuel pump has a black wire that supplies the ground to complete the circuit.

Remember that the computer does not source any power to actuators, relays
or injectors, but provides the ground necessary to complete the circuit. That
means one side of the circuit will always be hot, and the other side will go to
ground or below 1 volt as the computer switches on that circuit.


Diagram courtesy of AutoZone



Now that you have the theory of how it works, it’s time to go digging.

Look for 12 volts at the Orange/Lt. Blue wire (power source for fuel pump relay).
No voltage or low voltage, bad fuse link, bad wiring, bad ignition switch or ignition
switch wiring or connections. There is a mystery connector somewhere under the
driver’s side kick panel, between the fuel pump relay and the fuse link.

Turn on the key and jumper the fuel pump test connector to ground as previously
described. Look for 12 volts at the Light Pink/Black 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.

Check the Red/black wire, it should have 12 volts. No 12 volts there, either the
inertia switch is open or has no power to it. Check both sides of the inertia
switch: there should be power on the Red wire and Red/Black wire. Power on the
Red wire and not on the Red/Black wire means the inertia switch is open.

Make sure that the power is off the circuit before making any resistance checks.
If the circuit is powered up, your resistance measurements will be inaccurate.




You will have to drop the tank to inspect the pump power and ground connector
and the pump wiring chassis ground.

Pump wiring: Anytime the ignition switch is in the Run position and the test
point is jumpered to ground, there should be at least 12 volts present on the
black/pink wire. You should see less than 1 Ohm between the black wire(s)
and ground. The chassis ground is up near the spare tire shell. To get some
idea of what a good reading is, short the two meter leads together and
observe the reading. It should only be slightly higher when you measure
the black wire to ground resistance.

The Tan/Lt Green wire provides a ground path for the relay power. With the test
connector jumpered to ground, there should be less than .75 volts. Use a test
lamp with one side connected to battery power and the other side to the
Tan/Lt Green wire. The test light should glow brightly. No glow and you have a
broken wire or bad connection between the test connector and the relay. To test
the wiring from the computer, remove the passenger side kick panel and
disconnect the computer connector. It has a 10 MM bolt that holds it in place.
With the test lamp connected to power, jumper pin 22 to ground and the test
lamp should glow. No glow and the wiring between the computer and the fuel
pump relay is bad.

Computer: If you got this far and everything else checked out good, the computer is suspect.
Remove the test jumper from the ECC test connector located under the hood.
Probe computer pin 22 with a safety pin and ground it to chassis. Make sure the computer
and everything else is connected. Turn the ignition switch to the Run position and observe
the fuel pressure. The pump should run at full pressure.
If it doesn't, the wiring between pin 22 on the computer and the fuel pump relay is bad.
If it does run at full pressure, the computer may have failed.

Keep in mind that the computer only runs the fuel pump for about 2-3 seconds when you turn
the key to the Run position. This can sometimes fool you into thinking the computer has died.
Connect one lead of the test light to power and the other lead to computer pin 22 with a safety pin.
With the ignition switch Off, jumper the computer into self test mode like you are going to dump
the codes. Turn the ignition switch to the Run position. The light will flicker when the computer
does the self test routine. A flickering light is a good computer. No flickering light is a bad computer.
Remove the test jumper from the ECC test connector located under the hood.

Fuel pump runs continuously: The fuel pump relay contacts are stuck together or the Tan/Lt Green wire
has shorted to ground. Remove the fuel pump relay from its socket. Then disconnect the computer and use
an ohmmeter to check out the resistance between the Tan/Lt Green wire and ground. You should see
more than 10 K Ohms (10,000 ohms) or an infinite open circuit. Be sure that the test connector isn’t
jumpered to ground.
If the wiring checks out good, then the computer is the likely culprit.

Prior to replacing the computer, check the computer power ground. The computer has its own
dedicated power ground that comes off the ground pigtail on the battery ground wire. Due to
it's proximity to the battery, it may become corroded by acid fumes from the battery. It is a
black cylinder about 2 1/2" long by 1" diameter with a black/lt green wire. You'll find it up
next to the starter solenoid where the wire goes into the wiring harness

If all of the checks have worked OK to this point, then the computer is bad. The
computers are very reliable and not prone to failure unless there has been
significant electrical trauma to the car. Things like lightning strikes and putting
the battery in backwards or connecting jumper cables backwards are about the
only thing that kills the computer.
 

89CobraGT

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Thanks for the diagram Well I checked the wires in the truck I found one rubbing a little so I hope thats the culprit. I bypasssed the fuselink and the wire didnt burn up... but the fuel pump didnt turn on. I checked my codes I got 85 shift solenoid? I dont know what that means? and 96 fuel pump secondary circuit fault/ high speed fuel pump relay open. Does this mean my relay is effed I just changed it a few weeks ago. Thanks for any replies
 

jrichker

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Code 85 - CANP solenoid - The Carbon Canister solenoid is inoperative or missing. Check vacuum
lines for leaks and cracks. Check electrical wiring for loose connections, damaged wiring and insulation.
Check solenoid valve operation by grounding the gray/yellow wire to the solenoid and blowing through it.
The computer provides the ground for the solenoid. The red wire to the solenoid is always energized any
time the ignition switch is in the run position.

Charcoal canister plumbing - one 3/8" tube from the bottom of the upper manifold to the rubber hose.
Rubber hose connects to one side of the canister solenoid valve. Other side of the solenoid valve
connects to one side of the canister. The other side of the canister connects to a rubber hose that
connects to a line that goes all the way back to the gas tank. There is an electrical connector coming from
the passenger side injector harness near #1 injector that plugs into the canister solenoid valve. It's
purpose is to vent the gas tank. The solenoid valve opens at cruse to provide some extra fuel.
The canister is normally mounted on the passenger side frame rail near the smog pump pulley.



It does not weigh but a pound or so and helps richen up the cruse mixture. It draws no HP & keeps the
car from smelling like gasoline in a closed garage. So with all these good things and no bad ones, why not
hook it up & use it?


The purge valve solenoid connector is a dangling wire that is near the ECT sensor and oil filler on the
passenger side rocker cover. The actual solenoid valve is down next to the carbon canister. There is
about 12"-16" of wire that runs parallel to the canister vent hose that comes off the bottom side of the
upper intake manifold. That hose connects one port of the solenoid valve; the other port connects to the
carbon canister.
Purge valve solenoid:



The carbon canister is normally mounted on the passenger side frame rail near the smog pump pulley.
Carbon Canister:



Code 96 86-90 model Mustangs. KOEO- Fuel pump monitor circuit shows no power - Fuel pump
relay or battery power feed was open - Power / Fuel Pump Circuits. The fuel pump lost power at some
time while the ignition switch was in the run position.

Look for a failing fuel pump relay, bad connections or broken wiring. The fuel pump relay is located under
the Mass Air Meter on Fox bodied stangs built after 91. On earlier model cars is under the passenger
seat. On Mass Air Conversions, the signal lead that tells the computer that the fuel pump has power
may not have been wired correctly. See MAF - Mustang Mass Air Conversion - StangNet - The Mustang Network


Diagram courtesy of Tmoss & Stang&2birds


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.




86-90 Models:
Using the diagram, check the red/black wire from the fuel pump relay: you should see 12 volts or so. If
not, 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 Orange/Lt blue wire, it is the power feed to the fuel pump
relay & has a fuse link in it. Good voltage there & at the Pink/black wire, swap the relay.

 

89CobraGT

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ok I found the problem it was actually my immobilizer wires whoever installed it put a screw right in the center of the wires from some plastic trim and twisted the wires together lol no wonder I couldnt figure this out I was really starting to get mad. Unfortunatly Its mandatory here to get immobilizers in some cars.
 

ScottyB351w

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Where is the fuseable link for the fuel pump located? Sorry if ive over looked it but i have read several post about this link but none of them mention its location
 

jrichker

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87-93-5-0-mustang-fuse-links-gif.64326.gif

Fuse links come with a current rating just like fuses. A clue as to what current they are designed for is to look at the size wire they protect.

Choose the fuse according to the wire size.


Wire size current table:


18 gauge wire = 5-8 amps
16 gauge wire = 10-12 amps
14 gauge wire = 15-17 amps
12 gauge wire = 20-25 amps
10 gauge wire = 30-40 amps
8 gauge wire = 50-60 amps.

Keep in mind that the wire size in the chart is for the circuit itself, not the size of the fuse link. The packages of fuse link repair material you can get at the auto parts stores also will have a current rating on them.

Fuse link material is available at most good auto parts stores. There may even be a fuse link already made up specifically for your car. Just be sure to solder the connection and cover it with heat shrink tubing.

Heat shrink tubing is available at Radio Shack or other electronics supply stores.

See the video below for help on soldering and heat shrinking wiring. There is a lot of useful help and hints if you don’t do automotive electrical work all the time.

View: http://youtu.be/uaYdCRjDr4A
 

JerylJames

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Jul 16, 2016
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Hey jrichker I have a question... I noticed in your fuse link diagram you have 4 wires with fuse links going into the yellow 10 gauge that hooks up to solenoid. I have a 92 GT and there is only 3 fuse links on mine, it is missing the fuel pump (orange/lt blue) wire with fuse link. My question is, is the fuse link located else where?
 

jrichker

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Hey jrichker I have a question... I noticed in your fuse link diagram you have 4 wires with fuse links going into the yellow 10 gauge that hooks up to solenoid. I have a 92 GT and there is only 3 fuse links on mine, it is missing the fuel pump (orange/lt blue) wire with fuse link. My question is, is the fuse link located else where?
No. That is where the fuel pump picks up its power. Peel the covering over the wire bundle back and you will portably find the orange/lt blue wire.
 

JerylJames

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Jul 16, 2016
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@jrichker I tried the jump test connector you had on another thread and the fuel pump kicked on. Does this mean that the fuse link is still in good shape? The pump still doesn't prime on its own.... Also, another weird thing is I hook up a ODBII to pull codes and the computer won't send codes. Does this mean the pcm is faulty?
 

jrichker

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If the fuel pump runs when you jump the test connector, the fuse link is good.

All the 5.0 Mustangs from 86-95 were OBDI. An OBDII scanner won't wok on them.
What year car and engine do you have?

Dump codes sticky

Look at the top of the 5.0 Tech forum where the sticky threads are posted. One of them is how to dump the computer codes. Codes may be present even if the CEL (Check Engine Light) isn’t on. You don’t need a code reader or scanner – all you need is a paper clip, or if your lady friend has a hair pin, that will do the job.
I highly suggest that you read it and follow the instructions to dump the codes. http://www.stangnet.com/mustang-forums/threads/how-to-pull-codes-from-eec4.889006/
 

JerylJames

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@jrichker I'm sorry I meant OBDI... Its one of the code reader for Ford's. But I have a 92GT stock 302. I put in the svt 3g alternator, screamin deamon coil, msd black distributor, livewire plug wires, fuel pump and new 19lb injectors. I've upgraded little things like headlights, solenoid, radiator, headlight switch, sensors (iac, act, coolant). I changed the negative battery cable because it was all green and corroded. I talked to you a couple years ago about the same car and I figured out that the signal return was burnt out on the pcm so I soldered a little piece of wire. It ran really good for 2 years then a couple months ago I shut off after getting fuel and never started again.
 

Boostedpimp

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I would assume if you can't pull codes its a pcm problem. I've had it both ways where the fuel pump would constantly prime without stopping or no prime unless you jumped it. Both times it the trace in the pcm
 

jrichker

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@jrichker I tried the jump test connector you had on another thread and the fuel pump kicked on. Does this mean that the fuse link is still in good shape? The pump still doesn't prime on its own.... Also, another weird thing is I hook up a ODBII to pull codes and the computer won't send codes. Does this mean the pcm is faulty?
Computer will not go into diagnostic mode on 91-95 model 5.0 Mustangs

Revised Dec 23 2107
1.) To clarify signal ground connections on the engine mounted fuel injector wiring harness and add diagram for the engine mounted fuel injector wiring harness
2.) To add warning about using an automatic transmission O2 sensor wiring harness with a A9L manual shift transmission computer.


How it is supposed to work:
The grey/red wire (pin 46) is signal ground for the computer. It provides a dedicated ground for the EGR, Baro, ACT, ECT, & TPS sensors as well as the ground to put the computer into self-test mode. As long as you are successful dumping the codes by using the gray/red wire on the diagnostic connector for the ground when dumping, the computer’s internal ground on pin 46 is good.

If this ground is bad, none of the sensors mentioned will work properly. That will severely affect the car's performance. You will have hard starting, low power and drivability problems. Since it is a dedicated ground, it passes through the computer on its way to the computer main power ground that terminates at the battery pigtail ground. It should read less than 1 ohm when measured from anyplace on the engine harness with the battery pigtail ground as the other reference point for the ohmmeter probe.

Engine mounted fuel injector wiring harness sensors for a 5.0 mustang
63347.gif


What sometimes happens is that the test connector grey/red wire gets jumpered to power which either burns up the wiring or burns the trace off the pc board inside the computer. That trace connects pins 46 to pins 40 & 60.

OR

If an O2 sensor harness from an automatic transmission Mustang is used with an A9L manual shift transmission computer. The 12 volts from the automatic transmission starter circuit will damage the A9L computer.

The STI (Self Test Input) is jumpered to ground to put the computer into test mode. Jumpering it to power can produce unknown results, including damage to the computer. The ohm test simply verifies that there are no breaks in the wiring between the test connector and the computer input.

How to test the wiring :
With the power off, measure the resistance between the computer test ground (grey/red wire) on the self- test connector and battery ground. You should see less than 1 ohm.



If that check fails, remove the passenger side kick panel and disconnect the computer connector. There is a 10 MM bolt that holds it in place. Measure the resistance between the grey/red wire and pin 46 on the computer wiring connector: it should be less than 1 ohm. More than 1 ohm is a wiring problem. If it reads 1 ohm or less, then the computer is suspect. On the computer, measure the resistance between pin 46 and pins 40 & 60: it should be less than 1 ohm. More than that and the computer’s internal ground has failed, and the computer needs to be repaired or replaced.
While you have the computer connector disconnected from the computer, turn the ignition switch to the Start position and look for 12 volts on pin 46 of the computer wiring harness. If you see 12 volts then you have an automatic transmission O2 sensor harness. That will damage the A9L manual shift transmission computer.


See http://www.stangnet.com/mustang-forums/749974-computer-issue.html#post7490537 for Joel5.0’s fix for the computer internal signal ground.

If the first ground check was good, there are other wires to check. Measure the resistance between the STI computer self-test connector (red/white wire) and pin 48 on the computer main connector: it should be less than 1.5 ohms. More than 1 ohms is a wiring problem

The following is a view from the computer side of the computer wiring connector: it is for an A9L, A9P computer.
eec-iv-computer-connector-for-5-0-mustang-gif.gif


a9x-series-computer-connector-wire-side-view-gif.gif


Diagram courtesy of Tmoss & Stang&2birds

Check out the diagram and notice all the places the grey/red wire goes. Almost every sensor on the engine except the MAF is connected to it.

91-93 5.0 Mustangs




Complete computer, actuator & sensor wiring diagram for 94-95 Mass Air Mustangs
94-95_5.0_EEC_Wiring_Diagram.gif



See the graphic for the 10 pin connector circuit layout.
salt-pepper-10-pin-connectors-65-jpg.jpg



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
 

JerylJames

New Member
Jul 16, 2016
15
1
3
Washington
I would assume if you can't pull codes its a pcm problem. I've had it both ways where the fuel pump would constantly prime without stopping or no prime unless you jumped it. Both times it the trace in the pcm

What was your solution? And please don't say LS swap... lol j/k
 
Last edited:

JerylJames

New Member
Jul 16, 2016
15
1
3
Washington
@jrichker Ok I finally figured it out, my computer was corrupt. One of the 3 capacitors was bad so I am going to change them. But thanks for your detailed instructions and taking the time of day to reply and help. I owe you a beer or two or all of them... lol
 
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Blown88GT

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Nov 13, 1999
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@jrichker Ok I finally figured it out, my computer was corrupt. One of the 3 capacitors was bad so I am going to change them. But thanks for your detailed instructions and taking the time of day to reply and help. I owe you a beer or two or all of them... lol
Just so you know. AutoZone has replacement EEC's for $100 with core exchange. Almost doesn't pay to replace the caps yourself, since you get a fully reconditioned & tested ECU.
 
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