No Power

2MustangGTS · Jul 30, 2015

1989 Mustang GT convertible 5.0/5spd.

OK, I had no power and swapped in a new battery and ... started right up. This is what several of you suggested.

Oops, 4 days later dead battery.When I took it to the store they checked it and it had zero polarity. A open circuit killed it. OK, put another new battery in, saw a spark when just touching the positive cable to the post and pulled each fuse in the dash board and still get a spark when I touch the positive cable to the positive post. Pulled the wires to the alternator and a spark, pulled every wire connector apart I could, disconnected the power top motor and ... still a spark. Something is open, but where do I look or what do I do next?

mikestang63 · Jul 30, 2015

You could have a bad ground that is touching metal or a frayed power wire off the starter., a bad starter or solenoid. Time to break out the DVM and test light.

2MustangGTS · Jul 30, 2015

mikestang63 said:
You could have a bad ground that is touching metal or a frayed power wire off the starter., a bad starter or solenoid. Time to break out the DVM and test light.

I will give that a try, but the starter works fine and the solenoid is new. In fact I had 3 new solenoids and checked the system with each installed and ... no difference. I will be checking with a DVM but with all the fuses pulled and the spark still occurs, what is left? Non fused or able to operate when no key is in?

jrichker · Jul 30, 2015

Disconnect the fuse links and see if you still get a spark.

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.

Typically it is something draining the battery. Small things like glove box or courtesy lights are often the culprits. If you have an aftermarket stereo or alarm system, it is also suspect.

The ideal method is to disconnect the negative terminal, and connect a Digital Multimeter (DVM) between the negative terminal on the battery and the negative cable. Set the DVM on a low current scale of 2-5 amps if it doesn't auto range. Watch the current draw, and then start pulling out fuses. When you see a sudden drop in the current, that circuit is the likely culprit. Note that the computer, radio & clock will draw less than 1/10 amp to keep the settings alive.

See http://assets.fluke.com/appnotes/automotive/beatbook.pdf. You will need the Adobe Acrobat viewer which is also a free download – Adobe Acrobat Reader DC Install for all versions

If you can’t find the current drain by pulling fuses, then the alternator is suspect or any aftermarket sound or lighting equipment that may be on the car. Disconnect the alternator output power plug, then disconnect any aftermarket sound or lighting equipment while watching the current on the DVM.

Diagrams courtesy of Tmoss & Stang&2birds

Fuse box layout

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

T5 Cutaway showing T5 internal parts
http://www.veryuseful.com/mustang/tech/engine/images/5_Speed_Cutaway_Illustrated.jpg

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

2MustangGTS · Jul 31, 2015

jrichker said:
Disconnect the fuse links and see if you still get a spark.

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.

Typically it is something draining the battery. Small things like glove box or courtesy lights are often the culprits. If you have an aftermarket stereo or alarm system, it is also suspect.

The ideal method is to disconnect the negative terminal, and connect a Digital Multimeter (DVM) between the negative terminal on the battery and the negative cable. Set the DVM on a low current scale of 2-5 amps if it doesn't auto range. Watch the current draw, and then start pulling out fuses. When you see a sudden drop in the current, that circuit is the likely culprit. Note that the computer, radio & clock will draw less than 1/10 amp to keep the settings alive.

See http://assets.fluke.com/appnotes/automotive/beatbook.pdf. You will need the Adobe Acrobat viewer which is also a free download – Adobe Acrobat Reader DC Install for all versions

If you can’t find the current drain by pulling fuses, then the alternator is suspect or any aftermarket sound or lighting equipment that may be on the car. Disconnect the alternator output power plug, then disconnect any aftermarket sound or lighting equipment while watching the current on the DVM.

Diagrams courtesy of Tmoss & Stang&2birds

Fuse box layout

See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring Mustang FAQ - Wiring & Engine Info Everyone should bookmark this site.

94-95 Mustang wiring diagrams
Mustang FAQ - Wiring & Engine Info

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

Mustang 5.0 Lights and Radio schematic, by TMoss:

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

T5 Cutaway showing T5 internal parts
http://www.veryuseful.com/mustang/tech/engine/images/5_Speed_Cutaway_Illustrated.jpg

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

Thanks,
I did check the alternator and it does not seem to be the problem. When I disconnected the yellow wire from the solenoid no spark when I touched the positive cable to the post. I will be checking the systems this wire feeds tomorrow. I will also be using a volt meter as I know some current always flows and that does not indicate a problem, so time to look a little harder at the problem.

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