Engine New Pigtail White Wire Burn

Potomus Pete

Active Member
Mar 7, 2019
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Sarasota Florida
New Alt Pigtail Next White Wire Burn Had battery light on so I got new pigtail. Because the wires going into the connector wrere loose going in.. Carefully matched up wires. Started it up. Still had light. Pushed down the top wire round pigtail and heard the alt. strain. The white wire toasted. What happened???Nothing ever does go right with these cars .
 
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jrichker

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Mar 10, 2000
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@Potomus Pete

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
 

Potomus Pete

Active Member
Mar 7, 2019
208
71
38
55
Sarasota Florida
Hooked up a new alt. wired it up. No burn on the white. Im not good in any way with wires . Give me an idea on a regulator or something whats next in line. Checked grounds.
 

Potomus Pete

Active Member
Mar 7, 2019
208
71
38
55
Sarasota Florida
No pic is the fuselink the round cylinder by the starter sloenoid. if so can i bypass The white wire is the one that comes out of the alt. Comes out with the two orange and black.....
 

Blown88GT

Founding Member
Nov 13, 1999
1,584
282
124
Palm Beach Gardens, FL
That's an unusual fuselink to burn out. Bypassing any fuse is dangerous, could melt the harness & start a fire.
Did the alternator ever work? Need some history to figure out why it burned out.

You still have the 2G alternator with the external fan?
The power connection is the major point of failure.

Please write in complete sentences, this is not Twitter or F-Book.
 

Potomus Pete

Active Member
Mar 7, 2019
208
71
38
55
Sarasota Florida
My pigtail white yel. wire was loose causing occasional battery light. Went to replace it and white wire fried. Was perfect before. I dont know very upsetting. Replaced alt w /new. With new plug . Light still on. Alt not charging. Any ideas please... Cant find anything cooked by solenoid
 

jrichker

StangNet's favorite TOOL
SN Certified Technician
Mar 10, 2000
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Dublin GA
My pigtail white yel. wire was loose causing occasional battery light. Went to replace it and white wire fried. Was perfect before. I dont know very upsetting. Replaced alt w /new. With new plug . Light still on. Alt not charging. Any ideas please... Cant find anything cooked by solenoid
Turn the clock back about 66 years and my 1st grade report card had a check box for Listens to and follows directions. Mine always was marked Needs improvement. I sincerely hope that is not your problem.

The test and diagnose tech note I posted is all that you need. Do it step by step, do not skip steps, do not pick and choose what you want to do. Make sure that you have the required tools, a DVM or Multimeter, and printed copy of the tech note close at hand when you do the testing.
 

Potomus Pete

Active Member
Mar 7, 2019
208
71
38
55
Sarasota Florida
I have an 8th grade education sorry. Failed math from the day I was born. Ill take it to the shop. Most mechanical things I can do. Ball joints transmissions ect. Thank you very much.
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
13,542
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polk county florida
I'm kinda crappy with electrical stuff too, I just keep at it. I think you are missing something. You mechanic should be able to find it.
 

Potomus Pete

Active Member
Mar 7, 2019
208
71
38
55
Sarasota Florida
Back on the road......I used the old method that backyard mechanics have used for decades. I got my stubborn wife off the couch away from the F...n Facebook. Made her sit the the loud , hot foxbody and stare at the battery light while I messed with the wires. It was the other plug on top of the alternator. I guess the moral is replace 30 year old pigtails in pairs. Case closed , Thanks JESUS
 

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