Electrical electrical issue?

fredfifty

Active Member
Nov 23, 2011
299
59
49
SF Bay Area
cars acting up. i dont know if its the alternator or an mf switch or ?

car started up and i noticed the stock voltage meter was down to the white line just above the red. i turn headlights on and as soon as i turn the hazards on, car dies. i try to start her up again and nothing, no click no nothing....the startup lights on dash dont even come on (when i turn key to on but not start)...radio wont even come on when its on accessory. but the headlights still go on?!

battery reads 12.9v with car off. the date on the battery says 1/14...so could it be the battery on its way out?? the terminals are clean, connections clean, grounds intact. i should note this is an all of a sudden incident. meaning it was driving fine the past 6 months or so...now this?? hmm weird.

any idea stangnet?
 
  • Like
Reactions: Willstang86
  • Sponsors (?)


jrichker

StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
26,893
2,558
224
73
Dublin GA
Alternator troubleshooting for 86-93 5.0 Mustangs:

Never, never disconnect an alternator from the battery with the engine running. The resulting voltage spike can damage the car's electronics including the alternator.



Revised 28-Nov-2018 to add warning that the instrument cluster must be in place and working for the alternator to charge

Red color text applies to cars with a 3G alternator.

Do all of these tests in sequence. Do not skip around. The results of each test depend on the results of the previous tests for correct interpretation.

Simple first step: Remove the alternator and take it to your local auto parts store. They can bench test it for free.


Use a safety pin to pierce and probe the insulated connectors from the rear when doing tests with the connector plugged into its' mating connector.

Engine off, ignition off, battery fully charged.
1.) Look for 12 volts at the alternator output. No 12 volts and the dark green fuse link between the orange/black wires and the battery side of the starter solenoid has open circuited.
3G alternator: Look for 12 volts at the stud on the back of the alternator where the 4 gauge power feed wire is bolted.
No voltage and the fuse for the 4 gauge power feed wire is open or there are some loose connections.

2.) Look for 12 volts on the yellow/white wire that is the power feed to the regulator. No 12 volts, and the fuse link for the yellow/white wire has open circuited.

The alternator MUST have the instrument cluster in place and working properly. The alternator warning light is a part of the charging circuit. No cluster, then no working alternator.

Engine off, ignition on, battery fully charged
1.) The alternator warning light should glow. No glow, bulb has burned out or there is a break or bad connection in the wiring between the regulator plug and the instrument cluster. The warning light supplies an exciter voltage that tells the regulator to turn on. There is a 500 Ω resistor in parallel with the warning light so that if the bulb burns out, the regulator still gets the exciter voltage.
Disconnect the D connector with the 3 wires (yellow/white, white/black and green/red) from the voltage regulator.
Measure the voltage on the Lt green/red wire. It should be 12 volts. No 12 volts and the wire is broken, or the 500 ohm resistor and dash indicator lamp are bad. If the 12 volts is missing, replace the warning lamp. If after replacing the warning lamp, the test fails again, the wiring between the warning lamp and the alternator is faulty. The warning lamp circuit is part of the instrument panel and contains some connectors that may cause problems.

2.) Reconnect the D plug to the alternator
Probe the green/red wire from the rear of the connector and use the battery negative post as a ground. You should see 2.4-2.6 volts. No voltage and the previous tests passed, you have a failed voltage regulator. This is an actual measurement taken from a car with a working electrical system. If you see full or almost full12 volts, the regulator has failed.

Engine on, Ignition on, battery fully charged:
Probe the green/red wire from the rear of the connector and use the battery negative post as a ground. You should see battery voltage minus .25 to 1.0 volt. If the battery measured across the battery is 15.25 volts, you should see 14.50 volts

Familiarize yourself with the following application note from Fluke: See http://assets.fluke.com/appnotes/automotive/beatbook.pdf for help for help troubleshooting voltage drops across connections and components. .



You will need to do some voltage drop testing of several of the wires.

Start looking for these things:
1.) Bad diode(s) in the alternator - one or more diodes have open circuited and are causing the voltage to drop off as load increases. Remove the alternator and bench test it to confirm or deny this as being the problem.

2.) The secondary power ground is between the back of the intake manifold and the driver's side firewall. It is often missing or loose. It supplies ground for the alternator, A/C compressor clutch and other electrical accessories such as the gauges. Do the voltage drop test as shown in the Fluke tech note link. Measure the voltage drop between the alternator frame and the battery negative post. Watch for an increase in drop as the load increases. Use the Fluke voltage drop figures as guidelines for your decisions.

3.) Bad regulator that does not increase field current as load increases. Remove the alternator and bench test it to confirm or deny this as being the problem.

4.) Bad sense wire - open circuit in sense wiring or high resistance. The yellow/white wire is the voltage sense and power for the field. There is a fuse link embedded in the wiring where it connects to the black/orange wiring that can open up and cause problems. Disconnect the battery negative cable from the battery: this will keep you from making sparks when you do the next step. Then disconnect the yellow/white wire at the alternator and the green fuse link at the starter solenoid/starter relay. Measure the resistance between the alternator end of the yellow/white wire and the green fuse link: you should see less than 1 ohm. Reconnect all the wires when you have completed this step.

5.) Bad power feed wiring from the alternator. Use caution in the next step, since you will need to do it with everything powered up and the engine running. You are going to do the Fluke voltage drop tests on the power feed wiring, fuse links and associated parts. Connect one DMM lead to the battery side of the starter solenoid/starter relay. Carefully probe the backside of the black/orange wire connector where it plugs into the alternator. With the engine off, you should see very little voltage. Start the engine and increase the load on the electrical system. Watch for an increase in drop as the load increases. Use the Fluke voltage drop figures as guidelines for your decisions.


Alternator wiring diagram for 87-93 Mustangs.



The following are diagrams courtesy of Tmoss & Stang&2birds

Alternator wiring diagram for 94-95 Mustangs.


Voltage drops should not exceed the following:
200 mV Wire or cable
300 mV Switch
100 mV Ground
0 mV to <50 mV Sensor Connections
0.0V bolt together connections

Alternator wiring circuit
Notice the green wire connects to a switched power source. The circuit contains a 500 ohm resistor in series between the switched power and the alternator. Connecting it to switched power keeps the regulator from drawing current when the engine is not running. The resistor limits the current flowing through the wire so that a fuse isn't needed if the wire shorts to ground.

Also notice the sense wire connects to the starter solenoid and it is fused. It connects to the starter solenoid so that it can "sense" the voltage drop across the output wiring from the alternator.


Fuse link for 86-93 Mustangs
Replacement parts:
14 gauge fuse link for stock alternator.

Bussman BP/FL14 Fusible link
AutoZone

Dorman - Conduct-Tite 14 Gauge Fusible Link Wire Part No. 85620
Advance auto parts #85620
Pep Boys - SKU #8637594




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.

94-95 Mustang wiring diagrams
http://www.veryuseful.com/mustang/tech/engine/#95-95Diagrams

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:
http://www.veryuseful.com/mustang/tech/engine/images/mustangFoxLights-Radio_diag.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

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_Guide.jpg

Convertible top motor wiring http://www.veryuseful.com/mustang/tech/engine/images/mustang88VertTopMotorCkt.gif

Engine mounted fuel injector harness
http://www.veryuseful.com/mustang/tech/engine/images/mustangEngineHarness.gif

Location of the TPS, IAB, and the 10-pin connectors on a 5.0, picture by TMoss:
http://www.veryuseful.com/mustang/tech/engine/images/TPS_IAB_Pic.jpg

Starter circuit
https://www.stangnet.com/mustang-forums/attachments\21328

Alternator diagram for 94-95 Mustangs.
http://www.veryuseful.com/mustang/tech/engine/images/Mustang-94-95-Alt.gif
 
Last edited:
  • Like
Reactions: fredfifty

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
12,396
3,930
193
polk county florida
Guessing will get you stuck in a parking lot.
'I guess this plane will fly, it has an engine.'
Not trying to be mean or anything but you have to know what the condition of the battery is, it could have a shorted cell and will charge just fine but what it's time to send the juice to the starter it will give up nothing.
 

fredfifty

Active Member
Nov 23, 2011
299
59
49
SF Bay Area
Guessing will get you stuck in a parking lot.
'I guess this plane will fly, it has an engine.'
Not trying to be mean or anything but you have to know what the condition of the battery is, it could have a shorted cell and will charge just fine but what it's time to send the juice to the starter it will give up nothing.
im glad i found this problem arose as i pulled into the garage lol i will check the battery as well
 

fredfifty

Active Member
Nov 23, 2011
299
59
49
SF Bay Area
What;'s the voltage with the engine running?

Id pull the alt and head to your local parts store and have them test it.
unfortunately i cant start it to check...but when it was running (just before this whole thing happened) the stock volt meter on the dash was really low, almost to the red..id say between the white line and the red line
 

Olivethefet

Slap me as well as point and laugh
May 17, 2018
472
266
73
38
Enterprise AL
Whats throwing me off is the fact that the headlights will still come on but nothing on the dash comes on. Not even the radio. I get that the lights could come on and still might not even turn over the motor once. Also, the statement about not hearing any clicks or anything when the ignition is turned on sounds like something more than a bad alternator or weak battery.

Do the interior lights come on when you open the door? Have you checked all the fuses under the dash? I'm not sure if any of those fuses could cause a problem like this but it won't hurt to check.

If the headlights are on and you try to start the car do the lights dim? I doubt it because it doesn't sound like the system is engaging.

Has the factory wiring been monkeyed with? Specifically does it have a "sound system" in it?
 

fredfifty

Active Member
Nov 23, 2011
299
59
49
SF Bay Area
Whats throwing me off is the fact that the headlights will still come on but nothing on the dash comes on. Not even the radio. I get that the lights could come on and still might not even turn over the motor once. Also, the statement about not hearing any clicks or anything when the ignition is turned on sounds like something more than a bad alternator or weak battery.

Do the interior lights come on when you open the door? Have you checked all the fuses under the dash? I'm not sure if any of those fuses could cause a problem like this but it won't hurt to check.

If the headlights are on and you try to start the car do the lights dim? I doubt it because it doesn't sound like the system is engaging.

Has the factory wiring been monkeyed with? Specifically does it have a "sound system" in it?
interior lights come on when i open the door, even the key chime still sounds. headlights do not dim when i turn the key, also hi beam flash doesnt work, hi beam works only when i switch the multifunction arm forward to SET to hi beam. factory wiring is not hacked, i made sure of that. boggles me.
 

fredfifty

Active Member
Nov 23, 2011
299
59
49
SF Bay Area
on a whim decided to try and start car, it started. measured volts running, battery 14.4 and at alternator positive post 13-9-14.0. also ran codes and got 11 and 10.

wierd.
 
  • Like
Reactions: Olivethefet

jrichker

StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
26,893
2,558
224
73
Dublin GA
@fredfifty

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.







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



Saleen0679 was nice enough to dig this up for us awhile back: How to replace ignition switch on 1979-1993 Mustangs.
http://www.mustangandfords.com/how-to/engine/5657/


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
IgnitionSwitchWiring.gif


Fuel, alternator, A/C and ignition wiring
fuel-alt-links-ign-ac.gif


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
 
  • Like
Reactions: fredfifty

fredfifty

Active Member
Nov 23, 2011
299
59
49
SF Bay Area
ok i just ordered a motorcraft ignitiin switch $77 i hope that solves it. in the mean time i will load test batt and alt. thanks
 

Similar threads