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1991 4.0 Alternator Upgrade??


Kirby N.

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Monument, CO
Vehicle Year
1991
Make / Model
Ford
Engine Size
4.0
Transmission
Manual
My Alternator on my 1991 Ranger 4.0L is gone to crap.

I would love to install an over the counter 130 amp or 110 amp or something alternator from a later explorer. It looks like they would bolt right in but the wiring is different.

Can anyone tell me if there is another alternator that will work without mods or how I can mod the wiring? Here is what the plug looks like.



The black one will fit perfect, but the grey won't. The other plug doesn't at all. I have searched and come up with nothing.
 


Kirby N.

Active Member
Truck of Month
Joined
Jul 6, 2008
Messages
259
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78
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Location
Monument, CO
Vehicle Year
1991
Make / Model
Ford
Engine Size
4.0
Transmission
Manual
I figured it out. I took my alternator to a local alternator rebuilder.

Apparently, 1991 was a transitional year as far as alternators are concerned. They have a 2g alternator. The 2g cannot be rebuilt for more power. It also doesn't have any other options. It is a 65-80 amp alternator. No other options really However, with a little bit of wiring, it can take a 3g alternator, which has options up to 130amps.

I tried a bunch of 130 amp alternators. None had the correct mounting pattern. Some had the correct mounting pattern, but the wrong pulley. Some had no pulley.

Finally, I found and bought an alternator with the pulley that fit perfect.The right mounting pattern and a 6 groove pulley. It is for a 2004 Explorer 4.0 2wd. It has a lifetime warranty and was $130, about the same price as the replacement 70 amp for my ranger.

In case anyone else has a 1991, here is what I did:

Next, I removed the bigger 3 wire plug:





Next I added a terminal to the two red wires out of the plug. 2 wires to the one terminal. I used a copper end and soldiered it. Then shrunk wrapped it.

This fits on the post of the new alternator.

I didn't do anything with the other wire. The rebuilder said it was not needed? I suspect it is for the idiot light, but the idiot light did not come on.



Next I picked up this little plug (these can be purchased at you local auto parts store, I got it at the alternator place) and spliced it into the middle (white with black stripe) in the other plug.



Plugged everything in and boom! I got a cheap 130 amp alternator.
 
SCREWd2V

SCREWd2V

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Dec 4, 2009
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68
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Vehicle Year
1990
Make / Model
Ford
Engine Size
4.0
Transmission
Automatic
this alternator still working out okay for you? I have seen some pretty complicated writeups for the G2 to G3 130 amp alternator conversion. This is by far the simplest one I have seen
 
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