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stangboy said:

Ok, well I guess I have that part right. Thanks!

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Starter solenoid wiring for 86-91 Mustang



Starter solenoid wiring 92-93 Mustang or earlier Mustang with upgraded high torque mini starter.

stangboy said:

Hey guys! I was able to work on the car a couple times since my last update. Last week I realized I didn't have a sufficient block to chassis ground so ran a 2 guage wire from the back of the driver side head to the chassis. Once I did that the starter worked by turning the key instead of using a screwdriver on the solenoid. 1 small victory! yay! Still no power to the fuel pump or anything else for that matter. At that point I figured I'd get new fuel pump and PCM relays just to rule those out. They came in a few days later. So Wednesday night went back to try and solve the no start mystery....again. My buddy was on duty that day(he's a fellow firefighter) but his girlfriend, their 6 month old son and his 16 year old son were all home upstairs directly over the garage...just remember that tid-bit of info. My other buddy came over to help me with this wiring nightmare of mine.

Ok so I changed the relays and still no power to the fuel pump and nothing else is happening under the hood either. So I start checking for voltage starting from the ignition switch. Ignition switch had 12v. All the fuses in the fuse box were getting12v. Checked all the wires that have anything to do with the fuel pump. Only 1 wire going to the relay was getting power but it was less than 12v, if I remember correctly it was only about 5v. Also no power at the wire going to/coming from the PCM for the fuel pump but I check other random wires going to the PCM and they were getting 12v. So that tells me the computer is getting power. So we searched and checked plugs and other wires and traced wires trying to figure out why the fuel pump won't get power....nothing. So I decided to check the grounds that I had going to the firewall. They were good but there is one that came off of the TFI harness that the previous owner of the engine harness ran because I guess the ground wire in it got mess up somehow. Well after inspecting where it was spliced I found that one of the wires was hanging on my only 2 strands of wire. So I cut away the bad parts and respliced it with a new butt-connector. At that point we gave up on getting the fuel pump to come on by the key. So we just used the wire we had ran to jump it straight from the battery. When I turned the key to the on position the fuel guage worked....hmmm. So I turned the key back off and told Danny to listen to see if the injectors pulse when I turn it back on. They did.... "Then it should start" I said. I turned the key and now the starter won't turn. WTF man!! The only logical thing we could come up with was that maybe it got jammed up on the flywheel so I turned the crank a little just to alleviate that. Ok, I got back in the car to check and what do know not only did the starter work but the car started!!! Of course I had to immediately turn it back off because it was around 10:30 or 10:45 at night...remember that "tid-bit of info" I told you to remember. Yeah, so when I go back I'll start it back up a let her run and get some heat in her and check for leaks. Yes there will be pics and video. It's been a loooooong time coming. Now I'm excited and motivated again!

Sorry for dragging the story out but I wanted to paint a vivid picture so I had to tap into my inner @madmike1157

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Good for you man, what a satisfying feeling that must have been.

Dang grounding wires, especially to the computer.

Have fun with it tomorrow and I hope she runs fine for you.

stangboy said:

Hey guys! I was able to work on the car a couple times since my last update. Last week I realized I didn't have a sufficient block to chassis ground so ran a 2 guage wire from the back of the driver side head to the chassis. Once I did that the starter worked by turning the key instead of using a screwdriver on the solenoid. 1 small victory! yay! Still no power to the fuel pump or anything else for that matter. At that point I figured I'd get new fuel pump and PCM relays just to rule those out. They came in a few days later. So Wednesday night went back to try and solve the no start mystery....again. My buddy was on duty that day(he's a fellow firefighter) but his girlfriend, their 6 month old son and his 16 year old son were all home upstairs directly over the garage...just remember that tid-bit of info. My other buddy came over to help me with this wiring nightmare of mine.

Ok so I changed the relays and still no power to the fuel pump and nothing else is happening under the hood either. So I start checking for voltage starting from the ignition switch. Ignition switch had 12v. All the fuses in the fuse box were getting12v. Checked all the wires that have anything to do with the fuel pump. Only 1 wire going to the relay was getting power but it was less than 12v, if I remember correctly it was only about 5v. Also no power at the wire going to/coming from the PCM for the fuel pump but I check other random wires going to the PCM and they were getting 12v. So that tells me the computer is getting power. So we searched and checked plugs and other wires and traced wires trying to figure out why the fuel pump won't get power....nothing. So I decided to check the grounds that I had going to the firewall. They were good but there is one that came off of the TFI harness that the previous owner of the engine harness ran because I guess the ground wire in it got mess up somehow. Well after inspecting where it was spliced I found that one of the wires was hanging on my only 2 strands of wire. So I cut away the bad parts and respliced it with a new butt-connector. At that point we gave up on getting the fuel pump to come on by the key. So we just used the wire we had ran to jump it straight from the battery. When I turned the key to the on position the fuel guage worked....hmmm. So I turned the key back off and told Danny to listen to see if the injectors pulse when I turn it back on. They did.... "Then it should start" I said. I turned the key and now the starter won't turn. WTF man!! The only logical thing we could come up with was that maybe it got jammed up on the flywheel so I turned the crank a little just to alleviate that. Ok, I got back in the car to check and what do know not only did the starter work but the car started!!! Of course I had to immediately turn it back off because it was around 10:30 or 10:45 at night...remember that "tid-bit of info" I told you to remember. Yeah, so when I go back I'll start it back up a let her run and get some heat in her and check for leaks. Yes there will be pics and video. It's been a loooooong time coming. Now I'm excited and motivated again!

Sorry for dragging the story out but I wanted to paint a vivid picture so I had to tap into my inner @madmike1157

Click to expand...

There is nothing to be ashamed of w/regard to actually detailing what it is you've done so the the pics make sense, or that we can get a feeling for what you had to go through.

What I absolutely hate is:

"Don't have time to say what I actually did,...here's a few random pics......enjoy."

Good job buddy I was wondering where you were with this glad to see you makin head way again

stangboy said:

Ok guys I'm finally getting a chance to go back and start my car in the morning. The plan is to start it and let it run until it reaches operating temperature then shut it down and change the oil. Of course I'll be checking for leaks or strange noises while it's running. After that I'd like to wire in my fuel pump to one of the fuses in the fuse box since I can't figure out why I can't get power to it from the key. I was thinking the #18 fuse. It's a 20A fuse that has the Instrument cluster, Transmission control module, Constant control relay module, and ignition system on it. Would that be a good one to use? @jrichker ? @madmike1157 ?

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#1. And why are we changing the oil after start up? Unless you have contaminated the oil in some way w/ gas, or water/antifreeze,....leave it in there at least for the initial break-in (If it's a new motor).

#2. Buy a test light. They're cheap, and will tell you instantly which circuit is hot.

#3. as for which fuse,...I'm not the one to ask. I don't have a stock, (and haven't had ) a stock fuse panel on a Mustang since '12.

Fuel Pump Troubleshooting for 87-90 Mustangs

Revised 1-Dec-2015 to add fuse links diagram.

Clue – listen for the fuel pump to prime when you first turn the ignition switch on. It should run for 1-3 seconds and shut off. To trick the fuel pump into running, find the ECC test connector and jump the connector in the upper LH corner to ground.





Turn the ignition switch on when you do this test.


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 Mustangs built before 92. See the diagram to help identify the fuel pump relay wiring colors. Be sure to closely check the condition of the relay, wiring & socket for corrosion and damage.
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.

Control 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.


Power Path
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.

Fuse links


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. 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


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.



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

All voltage reading are made with one voltmeter lead connected to the metal car body unless otherwise specified

Check for 12 volts at the red wire on the inertia switch. No 12 volts at the inertia switch, the ignition switch is turned off or faulty or there is no power to the EEC (computer) power relay. To be sure look for good 12 volts on the red wire on any fuel injector.
Good 12 volts means the EEC relay is working. No 12 volts and the ECC wiring is at fault.
Look for 12 volts on the red/green wire on the ignition coil: no 12 volts and the ignition switch is faulty, or the fuse link in the ignition power wire has blown. No 12 volts here and the ECC relay won’t close and provide power to the inertia switch. Check the Red/black wire on the inertia switch, 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. Push the button on the side of it to reset it, and then recheck. Good 12 volts on one side and not on the other means the inertia switch has failed.

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.

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. With power off, check the pump ground: you should see less than 1 ohm between the black wire and chassis ground.



The yellow wire is the fuel tank sender to the fuel quantity gage. The two black wires are grounds. One ground is for the fuel tank sender and the other is the fuel pump. The ground for the fuel pump may be larger gauge wire that the fuel tank sender ground wire.

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 should see less than 1 Ohm between the black wire(s) and ground. 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. In extreme ghetto cases, the pump relay may have been bypassed. 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.

See the following website for some help from Tmoss (diagram designer) &
Stang&2Birds (website host)

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

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

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