Alternator won't charge - please help

5.0Droptop said:

I have no clue. I no longer have a mustang.

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I guess that answered that question....

jrichker said:

I guess that answered that question....

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Yeah. This was on my 91 vert i had a couple of years ago.

Why do some say to install the two black wires back on the alternator and other say not to and tape them up? I have a 4 gauge cable on it plus the two black wires.

BOSSC351 said:

Why do some say to install the two black wires back on the alternator and other say not to and tape them up? I have a 4 gauge cable on it plus the two black wires.

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How do you spelL F-I-R-E?
There is a whole world of people who are ignorant of basic electrical principles.


Under no circumstances connect the two 10 gauge black/orange wires to the 3G alternator. If the fuse blows in the 4 gauge wire, the two 10 gauge wires will be overloaded to the point of catching fire and burning up the wiring harness.

Here is the reasoning behind using only a single 4 gauge fused power feed to the alternator. If you use the two 10 gauge black/orange wires in addition to the 4 gauge wire, you have two fused power feed paths. The total current capacity of the wiring is the sum of the fused paths. The 4 gauge path is fused for 125 amps, and the two 10 gages wires are fused for 60 amps. That is a total of 185 amps, which exceeds the capacity of the alternator. Overload can occur without the fuses blowing, damaging the alternator.

The worst case scenario is that the alternator develops an internal short to ground resulting in a catastrophic failure. The initial short circuit surge current is limited by the resistance of the wiring. The current in a parallel circuit divides up according to the resistance of the branches. If the 4 gauge fuse opens up first, the two 10 gauge black/orange wires will be carrying the short circuit surge current. Depending on the time lag of the fuse links, they may open up before a fire starts or they may not.


http://www.stangnet.com/mustang-forums/threads/3g-alternator-install-a-how-to.646825/#post-6673702

Alternator wiring.






If you have a 3G alternator, the white/ yellow wire is critical to proper operation. It is the voltage sense and regulator power lead that picks up the difference in voltage at the alternator output stud and the connection point at the starter solenoid. If you cheat and run it directly to the alternator output, it sees the voltage at the alternator output stud. It does not see the voltage at the starter solenoid connection point where it feeds power to everything else. You may have a voltage drop in the wiring between the alternator output stud and the connection to the starter solenoid. Thus you may have low voltage or less than the standard regulated voltage at the starter solenoid connection point. This makes for low voltage throughout the rest of the car: everything operates at less than full efficiency.

Starter solenoid wiring 86-91 model cars.

Connect the fused 4 gauge wire to the alternator and the battery side of the starter solenoid.


Starter solenoid wiring 92-93 Model cars.

I thought I fixed my charging problem and a day later here it goes again. Getting 17-18 volts at the back of the alternator and its not making it to the battery. I suspect the signal wire to the alternator is not connected good hence the overcharging voltage. Im taking loose wires at each point this afternoon and combining them into one soldered lug at each point to make sure I am getting solid connections.

I have recleaned the batt negative cable ground to body and added a star washer to dig into the metal on the cable and body. I have verified my engine is grounded to the body good with a DVOM and I will add a star washer to it this afternoon. Alternator grounded good to the engine. Ground on DS shock tower good and will get a new star washer this afternoon.

jrichker said:

How do you spelL F-I-R-E?
There is a whole world of people who are ignorant of basic electrical principles.


Under no circumstances connect the two 10 gauge black/orange wires to the 3G alternator. If the fuse blows in the 4 gauge wire, the two 10 gauge wires will be overloaded to the point of catching fire and burning up the wiring harness.

Here is the reasoning behind using only a single 4 gauge fused power feed to the alternator. If you use the two 10 gauge black/orange wires in addition to the 4 gauge wire, you have two fused power feed paths. The total current capacity of the wiring is the sum of the fused paths. The 4 gauge path is fused for 125 amps, and the two 10 gages wires are fused for 60 amps. That is a total of 185 amps, which exceeds the capacity of the alternator. Overload can occur without the fuses blowing, damaging the alternator.

The worst case scenario is that the alternator develops an internal short to ground resulting in a catastrophic failure. The initial short circuit surge current is limited by the resistance of the wiring. The current in a parallel circuit divides up according to the resistance of the branches. If the 4 gauge fuse opens up first, the two 10 gauge black/orange wires will be carrying the short circuit surge current. Depending on the time lag of the fuse links, they may open up before a fire starts or they may not.


http://www.stangnet.com/mustang-forums/threads/3g-alternator-install-a-how-to.646825/#post-6673702

Alternator wiring.






If you have a 3G alternator, the white/ yellow wire is critical to proper operation. It is the voltage sense and regulator power lead that picks up the difference in voltage at the alternator output stud and the connection point at the starter solenoid. If you cheat and run it directly to the alternator output, it sees the voltage at the alternator output stud. It does not see the voltage at the starter solenoid connection point where it feeds power to everything else. You may have a voltage drop in the wiring between the alternator output stud and the connection to the starter solenoid. Thus you may have low voltage or less than the standard regulated voltage at the starter solenoid connection point. This makes for low voltage throughout the rest of the car: everything operates at less than full efficiency.

Starter solenoid wiring 86-91 model cars.

Connect the fused 4 gauge wire to the alternator and the battery side of the starter solenoid.


Starter solenoid wiring 92-93 Model cars.

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Damn, you are right! Damn damn damn!!! Right in front of my face and it never ever clicked this was a major catastrophe waiting to happen. THANKS!!!!!!

That signal wire comes out of the single connector recepticle at the back of the alternator and goes down with with the black/orange wires and is bundled in harness wrap then goes straight back to the alternator in the center pin of the 3 wire connector. I found where the black/orange comes out by the solenoid. it goes in to a rubber junction marked p13 along with a brown? wire and comes out as a green wire to the solenoid. There is no continuity there between the signal wire and the green wire. Now there is between the light green/red in the 3 wire connector and the green wire at the solenoid.

@BOSSC351

BOSSC351 said:

That signal wire comes out of the single connector recepticle at the back of the alternator and goes down with with the black/orange wires and is bundled in harness wrap then goes straight back to the alternator in the center pin of the 3 wire connector. I found where the black/orange comes out by the solenoid. it goes in to a rubber junction marked p13 along with a brown? wire and comes out as a green wire to the solenoid. There is no continuity there between the signal wire and the green wire. Now there is between the light green/red in the 3 wire connector and the green wire at the solenoid.

Click to expand...

Check out the diagram below of the alternator. The yellow/white wire goes to a fuse link that connects to the black/orange wire.

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 15 April 2012 to add simple check for regulator failure in Engine off ignition on, battery fully charged section, item 2.

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.

Engine off, ignition on, battery fully charged:
1.) Alternator warning light should glow. No glow, bulb has burned out or there is a break in the wiring between the regulator plug and the dash. The warning light supplies an exciter voltage that tells the regulator to turn on. There is a 500 ohm 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.




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.

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

I took the 4 gauge cable off the alt last night and soldered a new lug with the smallest hole I could find. 5/16 is it and it is making good contact. I took the black/orange wires off the alt and taped them up like suggested. Worked on this with my brother all afternoon. He is much better than I am at electrical troubleshooting. We still have no solution. We started off with a charged battery. Saw a possible issue with the original ground strap so we used a jumper cable to make sure we have a good ground on the engine and tried multiple points. Still no change. The alt starts out at 14 to 15 volts at the lug and after 5 minutes of idling goes up to 17-20 and at times higher. This is while using the chassie as ground because the battery is in the trunk. Now if we use the test ground on the back of the alt its 14.7 to 15. We found a starting voltage of 1 to 2 volts at the valve cover bolts and it gradually increases in 5 minutes to 4-6 volts. The intake shows voltage. Accy brackets show voltage. We looked for voltage leaks and isolated the plug wires away from the block. No difference. The only other power source around the block is the starter cable and it is completely wrapped with loom and secured from rubbing and movement. We also moved the starter battery feed wire to the trigger side of the fender starter solenoid so it is only live when the ignition is actuated to start the car. Slight improvement by about a tenth of a volt. The three things we have left to try are 1) again remove the alt and have it tested. 2) Replace the OEM ground strap with a larger one plus add another at the front of the block. 3) Run a 2 gauge ground from the battery in the trunk all the way up and hook it directly to the block just under the alt. We have really no other ideas what to do. We hooked the jumper cable directly to the alt and a ground and the issue remains. My brother jumped all around the car looking for bad grounds and voltage drops and of course there is a slight drop in the run to the trunk from the 125 amp megafuse but we are getting battery voltage at the drivers fender mounted solenoid where the signal wire samples from. Also the alt light function works. it activates with ign on byt eng off. Goes off when started. Comes on when the single white wire and connector is unplugged.

I am about ready to chunk this battery relocation kit and put my battery back up front where it started. I will have the alt tested again tomorrow after work and see what their machine says its putting out.

We are going to go after grounds first. Can't do anything but help our cause. 1 gauge from block to recommended sway bar mount. My current ground is totally insufficient as I have 2 gauge coming from the battery and the OEM 5.0 engine block ground to the chassis. Next will be the negative post on the battery attached to the passenger side quad shock mount instead of the body with 1 gauge. The jumper cable idea was ok but not when you figure in that it takes 4, 8 gauge wires to be equivalent to 1, 2 gauge wire. And we did NOT have that. Moving right along.....

Have you done the voltage drop testing with full load on the system as described in my previous post?

you DO have the stator wire hooked up right?

Added a 4 gauge ground wire and now im getting 14.4 to the battery and improved charging. Still getting 17 to 20+ fluctuating at the alt lug using chassis ground. 8 to 10 when grounded at the alt test ground bolt. Getting 3 to 6 volts at the valve cover bolt.

I will go through all the tests in your post again. That is how I found my alt bulb had gone out before. I am at work from 630 till 5 so my time is limited each day. I have several off days coming up and I will devote several hours to these tests and will post each reselt.

Alternator tested good. Oreillys has idiots working for them I guess. They showed a triple failure on their machine and 11 volts output after fumbling with the test machine and connectors guessing at each step. I got a second opinion from a man who has been rebuilding alternators and starters for 60 years. He took me back and showed me everything and its operation. He loaded it up to 135 amps and also showed me its output just past 14 volts saying where it was reading is considered perfect. I mentioned attaching a ground at the rear of the alt and he said I sould. I reinstalled the alt with a 2 gauge ground to my 2 gauge chassis ground on the block. No change. Im getting 17 to 20 volts at the lug. 14.5 at the battery in the trunk. Seems to be charging the battery but I still am concerned with the reading at the lug. Is it because the negative lead is attached to the body and not the negative post of the battery?