Electrical No charge from 3g alternator

[BigShowJoe]

I have been scratching my head (or more like beating it against the wall) on this. I upgraded to a 3g 130amp alternator and have never been able to get it to charge.

1991 LX 5.0

4gauge power wire from alternator directly to positive terminal on the battery (I've tried connecting it to both the positive side of the solenoid and directly to the battery).
D Plug:
Constant 12v on the yellow wire.
12v on the green/red wire with the ignition on and a slight drop to ~11.6 with the engine running.
White wire looped from the D plug to the stator plug.

With the engine off, the battery is reading 12v. With the engine running, still the same 12v.

If I disconnect the 4gauge power wire and test voltage directly at the back of the alternator with the engine running, it reads from 28 to 35 volts but as soon as that is connected back to the battery, only 12 volts.

What can stop the alternator from outputting voltage when everything is connected as it should be?

 

[Mcmahst]

Maybe it has a bad internal regulator? Isn’t that removable?

 

[BigShowJoe]

This is my third 3g alternator. All have behaved the same. It's something in the car.

 

[nickyb]

Did you follow the 3g swap instructions in the forum here? Its been a while since I've done mine but I do remember deleting the two small 10 gauge wires and I added a mega fuse.

 

[BigShowJoe]

You mean the two black/orange wires? I'm not using them.

 

[nickyb]

I don't know why but the how to for that is not coming up anymore???
Maybe some cookie counter can fix it?

 

[General karthief]

I don't know why but the how to for that is not coming up anymore???
Maybe some cookie counter can fix it?

Job for the janitor, I already tried, I'm a computer idiot.
@Noobz347

 

[Noobz347]

Resource icon

3G Alternator Fox Upgrade

Aug 2, 2013

3g Alternator Upgrade Into a Fox Mustang.

• Noobz347
• Installation Articles

 

[nickyb]

Maybe that white/ black stripe wire??????
Go over install again and I'm sure you'll get it to work.

 

[BigShowJoe]

I am wired exactly like the diagram below. If I remove the red wire from the battery the alternator is putting out 28-35 volts. With everything connected, I never see more than 12 volts.

 

[89ripper]

Be careful with those voltage spikes...you could possibly cause damage to some of the electronics.

9

Thread '3g Alternator Swap Problem'

Apr 6, 2015

so i did this 3g alternator swap on my 90 mustang 302 carbed. Everything works fine but after its all hooked up it drains my battery. I am sure its my alternator drainign it. Ive narrowed it down to the yellow constant wire on the plug i think. I hooked it to straight to the terminal post on the back since its supposed to be constant. When i have that wire unplugged it doesnt drain the battery but only runs at 12 volts insteadof about 15. Also noticed when it was unplugged the squeeking at hire rpms went away but when i pulgged it back in it started rite back up and it sounds to be coming...

• 90mustang347
• Replies: 6
• Forum: Fox 5.0 Mustang Tech

 

[BigShowJoe]

Be careful with those voltage spikes...you could possibly cause damage to some of the electronics.

9

Thread '3g Alternator Swap Problem'

Apr 6, 2015

so i did this 3g alternator swap on my 90 mustang 302 carbed. Everything works fine but after its all hooked up it drains my battery. I am sure its my alternator drainign it. Ive narrowed it down to the yellow constant wire on the plug i think. I hooked it to straight to the terminal post on the back since its supposed to be constant. When i have that wire unplugged it doesnt drain the battery but only runs at 12 volts insteadof about 15. Also noticed when it was unplugged the squeeking at hire rpms went away but when i pulgged it back in it started rite back up and it sounds to be coming...

• 90mustang347
• Replies: 6
• Forum: Fox 5.0 Mustang Tech

Yeah it was just a 5 second test to prove the alternator was putting out voltage. I just can't understand why it's not when everything is connected.

 

[89ripper]

Ok. I just worry when I hear stuff like that cause I seen some crazy stuff in my day. Follow some steps in that thread see if it helps you any

 

[nickyb]

Try and bypass the fusable links.

 

[AeroCoupe]

I’d also say hook the yellow wire up to the stud on the alt va the battery.

 

[toasterboy1]

Have you tried a different ignition on source for you green wire? Read that if the dummy light burns out it kills the voltage to signal the alternator. I ran into a similar problem when I converted to a digital dash cluster. There was not voltage on the green wire. Tapped into a different wire and magically 14+ while running.

 

[Jarhead67]

I am wired exactly like the diagram below. If I remove the red wire from the battery the alternator is putting out 28-35 volts. With everything connected, I never see more than 12 volts.

What kind of volt gage are you using?

 

[AeroCoupe]

Stock alternator light is paralleled by a 510 ohm resistor so the alternator will continue to charge if the light bulb burns out.

 

[toasterboy1]

Stock alternator light is paralleled by a 510 ohm resistor so the alternator will continue to charge if the light bulb burns out.

Very true. I would check the voltage on the green wire regardless. Never know the resistor is not fail proof.

 

[AeroCoupe]

Correct and correct. It's even more of a pain if you use a LED for the alternator light.