Electrical Need help please! No spark, Fuel pump not priming, and a mystery wire.

7991LXnSHO · Mar 28, 2013

I nominate jrichker for a " favorite tool" of the year award for 2013 if he has room on the mantle!

jrichker · Mar 28, 2013

7991LXnSHO said:
I nominate jrichker for a " favorite tool" of the year award for 2013 if he has room on the mantle!

Thanks for the vote of confidence. It remains to be seen if the WunderKid (I wonder if this will fix it) will actually find and fix the problem...

15reidna · Mar 28, 2013

Is the fuel pump relay coil the same thing as the relay under the drivers seat?

15reidna · Mar 28, 2013

Alright hopefully the problem is the fuel pump relay coil but I don't know what the relay coil does, where it is, what it looks like, or how to fix it. Is it by the EEC?

jrichker · Mar 28, 2013

Do you have 12 volts on the red/green wire with the ignition switch in the Run position.? Yes/No

15reidna · Mar 28, 2013

Just checked and I still don't have any voltage reading in the red/green wire in the ignition switch.

jrichker · Mar 28, 2013

15reidna said:
Just checked and I still don't have any voltage reading in the red/green wire in the ignition switch.

Then replacing the fuel pump relay will not fix the problem.

You MUST have 12 volts on the red/green wire with the ignition switch in the Run position for any part of the fuel system, ignition system or computer system to work properly.

Accessing the ignition switch to test the voltages:
There are 2 other screws in the lower dash cover that need to be removed

The ignition switch is under the plastic cover on the steering column. There are 3 long screws that secure the top and bottom parts of the plastic cover. The screws are located in th bottom cover.

Using the diagram below, look for 12 volts on the red/green wire with the ignition switch in the Run position. Measure it right at the switch.

Diagram courtesy of Tmoss & Stang&2birds

Good 12 volts on the red/green wire at the switch with the ignition switch in the Run position, then the switch is good.
The problem is in the fuse link located in the wiring harness.

No 12 volts at the red/green wire at the switch with the ignition switch in the Run position, then check the yellow wires going to the switch.

Good 12 volts on the yellow wires, then replace the ignition switch.
No 12 volts on the yellow wires, then the fuse link shown in the diagram above is blown open.

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.

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

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

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

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

15reidna · Mar 29, 2013

I have no volts going to the red/green wire and I do have power to both yellow. I already replaced the ignition switch though so I don't think that its bad already. At this point I'm thinking that a mouse has chewed through a wire somewhere.

88LX5.Oh · Mar 29, 2013

So according to the diagram JR supplied you with, what you're saying is, you're getting power TO the ignition switch (big yellow wires are main power wires for switch), but you're not getting any power to the ignition coil. Is this correct?

jrichker · Mar 29, 2013

NO 12 volts on the red/green wire AT the ignition switch itself? Are you sure the switch is properly engaging the key lock mechanism?

15reidna · Mar 29, 2013

Yes, No 12 volts to the red/green wire and I just checked the ignition coil and didn't get anything out of that either. Which is weird because the ignition coil is also brand new.

jrichker · Mar 29, 2013

You MUST have 12 volts on the red/green wire with the ignition switch in the Run position for any part of the fuel system, ignition system or computer system to work properly. It doesn't matter if it is a new part or an old part, no 12 volts on the red/green wire with the ignition switch in the Run position no worky, no matter what.

If you do not have 12 volts AT the ignition switch with it in the Run position and DO have 12 volts on the yellow wire, then there are 3 possibilities:
1.) You forgot to turn the ignition switch on, or did not turn it far enough to get it to the Run position.
2.) The slider bar that moves the ignition switch isn't engaging the switch properly.
3.) The ignition switch is defective or the parts house sold you the wrong switch.

The correct ignition switch looks like this:

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

15reidna · Mar 29, 2013

Just replaced all the fusable links with actual fusable links from autozone instead of just having them bipassed and wuala! She runs again and runs better then ever! Thanks for all your help!! I probably would have never found it without your help. Thanks.

jrichker · Mar 30, 2013

I am certainly glad to hear that you got it fixed. Enjoy your ride.

mustang mike 5.0 foxbody · Feb 21, 2016

I have the same problem but i do have power to both red green and yellow ignition coil except Eec red green nor injectors red wire how did you replace the fuseable links ? To red and green ?

jrichker · Feb 22, 2016

mustang mike 5.0 foxbody said:
I have the same problem but i do have power to both red green and yellow ignition coil except Eec red green nor injectors red wire how did you replace the fuseable links ? To red and green ?

Start you own post and I will help you. Snagging someone else's post is like taking food off their plate.

7991LXnSHO · Feb 23, 2016

Hey, Mr. Richler, look, it's the Goodyear Blimp! (As I steal a French fry.)

Electrical Need help please! No spark, Fuel pump not priming, and a mystery wire.

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