91 5.0 Alternator Not Charging - Checked Most Obvious

[koala33]

91 Foxbody 5.0 - 36K miles - mostly stock, no electrical upgrades etc...

Jrichker has posted several times a step-by-step checklist:

http://www.stangnet.com/mustang-forums/threads/91-alternator-not-charging-tested-alt-good.881078/

Before I start this list, is there anything else that I should check?

It started this yesterday when my battery light came on. I used a DMM and measured 12v at the battery while running. The next time I started it, it wouldn't start (not surprisingly).

I started by taking off the alternator and taking it to to a local auto parts store (AAP). They ran a test twice, and both times it said my alternator was "good".

I went home, put the alternator back on and took my battery for an exchange (was last replaced 4 years ago). I put the new battery in, and same thing - won't hold a charge. The guy ran a test with the car running, surging etc (I've uploaded the readout).

Next thing I did was go to the local parts store and bought an alternator and voltage regulator harness. I was told these harnesses can get bad over time. I replaced the alternator even though mine checked out fine - you never know.. Still no luck. So I boxed that up and put my OEM alternator back on. I cut the OEM wiring harness and soldered on a new one. Still no luck.

So the problem is not:

Voltage regulator wiring harness
Alternator
Voltage regulator (a new one comes attached to the new alternator)
Battery

I need to look up an all inclusive list where all the grounds on the car is and check that they are clean and tight.

I don't have a light meter, so I will have to get one tomorrow to follow Jrichker's step-by-steps.

Any other ideas before I start? My battery light functions fine. A while ago I did change out my OEM bulbs in the cluster to LED - somehow the cluster seems to be tied to malfunctioning electrical, but I don't think this has anything to do with it.

Earlier I checked the Green/Red wire on the voltage regulator harness, and I think it was reading 12.5v with the key on.

Maybe the stator harness is bad? Can't seem to find a local parts store in Northern VA, so may have to order this. Trying to get this fixed by Tuesday, but not sure how this is all going to pan out.

Any help is appreciated--

--Shawn

 

[koala33]

Results with OEM alternator and new battery.

Maybe easier to read here (zoom in):

https://drive.google.com/file/d/0B87jOqGHfdmGeVZjVlJqNEZlZVE/view?usp=sharing

 

[jka]

Battery voltage with the engine at idle should be 13.4-14.5 volts if the alternator is good. If your voltage was 12 volts then the alternator is not charging your battery with the engine running. Who checked it for you? ...because 12 volts is too low while the engine running and will not charge the battery.

 

[koala33]

Advance Auto Parts. I watched the guy while he did it. I put in another rebuilt alternator from Autozone and still got the same result. So unless the test was incorrect AND I bought a faulty alternator..

 

[koala33]

What's preventing alternator from charging battery?

 

[jka]

The alternator is not charging the battery..i think the test was right ..but the guy at advance auto was wrong. I have seen new alternators that turned out to be bad test good ..because the guy didn't know how to test them. I had to take back my alternator 3 times to auto zone before i got a good one... and each time they told me it was good. When i tested it myself with the engine running the volts on my voltmeter was all over the place. But trust me if you don't see 13.5 -14.5 volts at the battery while the engine is running then the alternator is not doing it's job.

 

[90lxwhite]

Not long ago I was having alternator troubles and it turned out that the pigtail wire was fried. It took me two alternators before I figured it out. The 1st one lasted a day or 2 and the 2nd one lasted about a day before it crapped out. When I took the 2nd one back to oriley's they tested it and said it was good and didn't want to honnor the warranty until I argued a little. Touch your alternator when the engine is cold, if it's hot the it's no bueño and a crap wire is the culprit. Parts store re-man alternators used to come w a new pigtail but now they don't it seems.

 

[koala33]

Not long ago I was having alternator troubles and it turned out that the pigtail wire was fried. It took me two alternators before I figured it out. The 1st one lasted a day or 2 and the 2nd one lasted about a day before it crapped out. When I took the 2nd one back to oriley's they tested it and said it was good and didn't want to honnor the warranty until I argued a little. Touch your alternator when the engine is cold, if it's hot the it's no bueño and a crap wire is the culprit. Parts store re-man alternators used to come w a new pigtail but now they don't it seems.

When you say pigtail wires... The voltage regular connector or stator connector (or so it's referred to as although that's never what it shows up on anyone's computer in the store)?

I changed the voltage regulator connector last night and still same thing. I'd LOVE for it to be the other connector that attaches to the alternator. Just gotta find that piece locally to save time - not sure there are any O'Reilly stores in Northern VA.

http://www.latemodelrestoration.com/item/LRS-14290B/86-93-Mustang-Alternator-Rectifier-Plug

 

[Boosted92LX]

I've bought both pigtails at O'Reilly. If you're not near one, here's the other on ebay:

http://m.ebay.com/itm/230784853736?nav=SEARCH

 

[koala33]

Which one did you buy from O'reilly? I am having a hard time finding it on their site.

 

[Boosted92LX]

Which one did you buy from O'reilly? I am having a hard time finding it on their site.

Well I bought the plug I linked you from ebay first. (bought it at Oreilly) They stock a dorman part for both. It turned out being the wrong one and I went in and had an employee find the one I needed in his system. I used to have the part numbers, but I'm not sure where they are now. If I can find them, I'll post them up.

 

[Boosted92LX]

here's one:

http://www.oreillyauto.com/site/c/d...k=Search_01539_1133918_406&pt=01539&ppt=C0330

The other:

http://www.oreillyauto.com/site/c/d...k=Search_01497_1133918_406&pt=01497&ppt=C0330

hope this helps.

 

[koala33]

Perfect, it is the second one that I need. Thanks a ton.

 

[Boosted92LX]

Perfect, it is the second one that I need. Thanks a ton.

No sweat brother.

 

[koala33]

So starting the Jrichker test...

Battery from + to - sits at 12.38 right now.

Rectifier connecter black and orange wires both measure 12v.

Voltage regulator connector white and yellow wire measures 12v.

Is it safe to assume that at this point that because the w/y wire on the voltage regulator connector has 12v, then the rectifier connector with the 2 b/o wires is doing its job (i.e. the connector is not faulty)?

 

[koala33]

With ign on, g/r wire for voltage regulator measured 11.5v. Could that be the issue? In the step-by-step, says should be 12.

With the ign on and D connector for voltage regulator plugged into the alternator, the battery light DOES come one. When I unplug the D connector with ign on, there is no battery light.

Probing the g/r wire on the D-connector (plugged in/ign on) gives me 2.33v.

 

[koala33]

I'm running out now to buy some probes for my DMM (rather than safety pins that aren't working very well), trickle charger, and light meter. If anyone could look at what I've done so far and let me know if anything looks suspicious, that'd be awesome. Right now my battery is sitting at 12.16 ign off, and 11.85 ign on. Going to try to do some enging running tests, but need to get some more juice in the battery.

Thanks a ton!

Shawn

 

[jrichker]

With ign on, g/r wire for voltage regulator measured 11.5v. Could that be the issue? In the step-by-step, says should be 12.

With the ign on and D connector for voltage regulator plugged into the alternator, the battery light DOES come one. When I unplug the D connector with ign on, there is no battery light.

Probing the g/r wire on the D-connector (plugged in/ign on) gives me 2.33v.

Your voltage readings are close enough that they shouldn't be a problem.

1.) Disconnect the battery negative terminal.
2.) Next set the DVM or Multimeter on low ohms.
3,) Disconnect the stator (AKA power plug) from the alternator .
4.) Measure the resistance from the black/orange wires on the stator plug to the battery positive terminal. You should see less than 1.0 ohm. More that that would suggest problems with the fuse link.

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

 

[koala33]

I am getting 3.55 K Ohm on each of the black/orange wires. So.. Maybe you've helped me find my problem? I don't think my DMM has a "low ohm setting", just ohms, but I am assuming this is the correct reading.

Also, I am not sure if I should be able to test for continuity between the + bat terminal and the b/o wires - I tried, no luck..

 

[koala33]

Also wanted to post a picture of the power cable with b/o wires.. As I said before,

"Is it safe to assume that at this point that because the w/y wire on the voltage regulator connector has 12v, then the rectifier connector with the 2 b/o wires is doing its job (i.e. the connector is not faulty)?"

Can I rule out a faulty connector? The insulation that you see is gummy. I am able to pretty easily poke a pin inside of it.

I did buy the fusible links at AZ just in case. Looks like I am going to have to unwrap the entire b/o wires to check for faults? These run all the way to the solenoid near the drivers side/firewall correct? Is that where the fusible links are?

Thanks,

Shawn