Alternator won't charge - please help

Call PA Performance...www.pa-performance.com/

If it is a regular 3G here's the wiring diagram.

[On a Mustang 86-93, the stator wire is the small white/black wire in the same plug as the two larger black.orange wires.

Remove the negative cable from the battery for safety reasons.

Black/orange wires get taped up out of the way and not used. Do not remove or mangle the plug on the end of the wires.

Small 3 wire plug used as is, no changes. It plugs into the same connector on the new alternator.

White/black wire on the plug where the Black/orange wires connect gets insulation stripped from it. Splice another wire onto it to make a Y. Solder the connection and use heat shrink tubing on it to cover the splice joint. Crimp a female 1/4" push on terminal on the new wire or use a connector from an old wiring harness.


Plug the 3 wire plug into the alternator.

Plug the white wire you spliced the into the little tab on the alternator.



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


Starter solenoid wiring with a Mini starter or 92-93 5.0 Mustang


I ran the 4 gauge wire under the front of the engine next to the 4 gauge wire for the starter power feed.
It came up the same path as the fuel injector supply lines, and gets bolted to the power output lug of the 3G alternator. The 125 amp fuse is mounted on a plastic panel bolted to the stock ignition coil mounts. One of side of the fuse has a 4 gauge wire connected to the battery side of the starter solenoid & the other to the 4 gauge power feed wire for the alternator.
Reconnect the battery negative cable.

Wiring is now finished. Check to make sure it is all neat and clean and everything is out of harms way. Start the car and check your voltage.

I had some 1" silicone aircraft heat shield tubing that I fed the 4 gauge alternator power feed wire through and tie wrapped & clamped it in place with some aircraft cushion clamps. That provided the wire extra protection from road debris and rocks. Some heater hose could be used to do the same thing.

I have an additional 4 gauge ground running from the power steering pump mount to the common chassis ground being pointed to in the photo.

Picture courtesy timewarped1972

Apart from the grinding I did on the mount bracket, there wasn't much to it. Rather than just grind a notch, I ground the whole web back to the thick part of the bracket. It looks much more factory that way.

See WWW.partsexpress.com for the fuse & fuse holder.
Fuse @ $3.90 each (need one) http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=071-952

Fuseholder @ $5.80 each (need one) http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=263-630

4 gauge black wire @ $1.95 a foot (use string to lay out routing & determine length) http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=100-196

4 gauge red wire @ $1.95 a foot (use string to lay out routing & determine length) http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=100-194

4 gauge ring crimp terminals (package of 5) $3.25. http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=095-584


3/4 “ Black heat shrink tubing, 4ft length, $3.56
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=082-058

3/4 “ Red heat shrink tubing, 4ft length, $3.56
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=082-064

Pre-fab 4 gauge cables with lugs already on the ends are available in most auto parts stores. Look for the starter switch to starter cables.

3G tech data:

See http://www.geocities.com/smithmonte/Auto/3G_130A_Alternator_Upgrade.htm - all the tech data you could ever want to know
OR
http://www.mustangcentral.net/tech/alternator.html - excellent pictures of installation/MustangFuseBox.gif[/url]

astrohell85 said:

The alternator in my 90 5.0 notchback won't charge. It's a PA Performance 3g 130 amp unit, about 2 years old and checks out fine at the parts stores tester. My battery is new (interstate) and checks out good also. I've replaced the battery cables and upgraded the alternator cable in the last two years also, all connections are clean. It's like the alternator isn't sensing low voltage, the battery light is on while running and it goes out if I unplug the wire from the alternator so I assume that circuit is fine, no shorting. Is there another bulb that the alternator uses to sense voltage drop? Everything was working fine, then one day i started it up and the battery light came on showing low voltage. Any help would be greatly appreciated.

Click to expand...

My PA performance 3g went bad on me. The battery light came on also. It wasnt low on voltage it was over charging which caused the light to come on. Put a voltage meter on the battery and check it out.

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.

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.

Alternator troubleshooting for 86-95 5.0 Mustangs:
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 regulator. This is an actual measurement taken from a car with a working electrical system.

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 voltage measured across the battery is 15.25 volts, you should see 14.50 volts

Diagram courtesy of Tmoss & Stang&2birds


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.

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

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

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 & pinout
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

check to make sure the resistor in the back of the cluster is connected properly, and that all the connections are tight and no corrosion.

jrichker, Thanks for the very informative thread. I am having issues with my 88 GT charging system and I have followed your guide for trouble shooting. I've made it this far:

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 regulator. This is an actual measurement taken
from a car with a working electrical system.

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 voltage measured across the battery is 15.25 volts, you should see 14.50 volts

When I probe the green/red wire at the rear of the connector and using the negative post as the ground I am only seeing 3.2 volts instead of the battery voltage minus .25 to 1.0. What do I need to be looking for? This problem is giving me fits!! Thanks in advance!!!!!

63onair said:

jrichker, Thanks for the very informative thread. I am having issues with my 88 GT charging system and I have followed your guide for trouble shooting. I've made it this far:

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 regulator. This is an actual measurement taken
from a car with a working electrical system.

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 voltage measured across the battery is 15.25 volts, you should see 14.50 volts

When I probe the green/red wire at the rear of the connector and using the negative post as the ground I am only seeing 3.2 volts instead of the battery voltage minus .25 to 1.0. What do I need to be looking for? This problem is giving me fits!! Thanks in advance!!!!!

Click to expand...

Is the alternator warning light illuminated on the instrument cluster?
Does the warning light turn on and off at all?

jrichker said:

Is the alternator warning light illuminated on the instrument cluster?
Does the warning light turn on and off at all?

Click to expand...

Mine is doing the same thing. The warning light will turn on and stays on.

Jrritter said:

Mine is doing the same thing. The warning light will turn on and stays on.

Click to expand...

Since there could be any number of things causing the problem, I suggest that you go back and work your way through the test path I posted in his thread. Then if you cannot find the problem, make your post.

88GT w/351 C swap. 3G alternator upgrade from Mr. Alternator from way back when they first appeared. Batt just tested out good. Alternator tested good. Starts out at about 14.3 V when running and depletes the battery and this reading falls gradually. Starts initially just fine with a charged battery but then drags the next time after it idles for a bit. First let me say thank you for posting this. I am down to testing the green/red wire for batt voltage. I messed up and turned ignition off and had nothing. I now have batt voltage. I pulled the cluster and removed the bulb that was out. The bulb and holder showed open. I removed the bulb from the holder and it showed good. Reinstalled it and now it shows good in the holder. I checked all the cluster bulbs and found another with similar issues. I am now replacing all the bulbs. I also tested the resister at the 2k scale on my Fluke. It shows .577. I can't imagine one little bulb will make the charging system inop. Next I will test out the green/red wire from cluster to alternator if the bulb changes don't fix it I don't know what else to do. Worked fine 1 year ago with no issues then this starts.

I accidentally unplugged a wire plug in located just under the starter solenoid one time and the alt quit charging. Its been years i cant recall which plug it was. But i think it was axsingle wire round plug.

I edited my original post because I had turned the ignition off for the test. Green/red shows voltage now and I now have an AMP red light on the cluster.

I have 4.7 volts from the rear of the plugged in connector at the green/red wire.

With the engine running I am seeing 14.1 to 14.3 at the battery and 14.6 to 15 at the green/ red wire.

Also it is pertinent to mention I have a battery box in the trunk. I measured voltage before the Maxi fuse junction at the ps shock tower, after, and at the battery. Im losing about .1 from front to rear.

5.0Droptop said:

I accidentally unplugged a wire plug in located just under the starter solenoid one time and the alt quit charging. Its been years i cant recall which plug it was. But i think it was axsingle wire round plug.

Click to expand...

I dont believe I have that connector anymore. All of my EFI harness was pulled for the swap. I believe the connector you are talking about was a ground.

5.0Droptop said:

I accidentally unplugged a wire plug in located just under the starter solenoid one time and the alt quit charging. Its been years i cant recall which plug it was. But i think it was axsingle wire round plug.

Click to expand...

What color is the wire and stripe? They help tell what circuit the wire is for. Please post the results.

Im trying to resolve any issues before converting from carburetor to the FiTech EFI system. No sense in compounding and confusing issues .

jrichker said:

What color is the wire and stripe? They help tell what circuit the wire is for. Please post the results.

Click to expand...

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