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Hello. My vehicle is a 1981 vw rabbit pickup 1.6l diesel no turbo. Picked up a brand new alternator for the truck. Put it on and all it does is squek and is not charging the battery. I have unplugged the alternator and it will stop squeaking. I have also tested the volts at the alternator with it unplugged. It makes 14.5 volts. I don't know the problem. Anything will help. Thanks
 

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I don't know much about alternators but I think that the squealing is caused by the belt slipping. Try tightening the belt.
 

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The belt is not slipping. Sure of that because I checked with the manual. And the battery isn't reading 14.5 volts it's reading 12.4 and falls. The alternator reads 14.5 volts at the plug
 

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Noisy alternator could be bearings or diode failure, if it is not a loose belt.

Spin the alternator pulley by hand with no belt on, of course, and it should be quiet smooth for a new unit. That rules out bearing problems.

Diodes can be tested with an electronic charging system diagnostic unit, or a voltmeter set to measure AC ripple. Your local auto parts store might do a free test for you with one of the electronic testers, like a Midtronics.

Not a good idea to run the alternator with it unplugged, and definitely do not unplug it while it is running. Do your tests at the plug with the harness plugged in.

If the alternator is showing over 13.5+ something volts, it is charging, you should see nearly the same voltage at the battery, minus no more than 2/10th's volt for voltage loss along the cable between the alternator and the battery.

If you are not getting voltage similarity at the battery, and it sounds like you are not, you have a loose, disconnected, or corroded harness between the alternator and the battery.

If you are getting charging voltage at the battery, but voltage falls off after the car is shut off, the battery has failed or it is draining from a short somewhere, even possibly through the alternator because of failed diode(s).
 

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Update: got the alternator to stop squealing, belt was Infact too loose. Now my problem is at the battery it only reads 13.1 volts at idling and 14.5 volts at the alternator idling. Bad ground somewhere? Please help
 

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Update: got the alternator to stop squealing, belt was Infact too loose. Now my problem is at the battery it only reads 13.1 volts at idling and 14.5 volts at the alternator idling. Bad ground somewhere? Please help
I would start by asking if you are using the same ground point when testing.

If you use the same ground point and read 14.5 one place and 13.1 then you have a voltage drop between the Alternator and the Battery.
I would first ask a few questions.

1. Have you replaced the ground cables from your battery to the Fram and from the frame to the engine/tranny depending on where it is mounted?
If you answer no, or I changed the end, then I would replace the cables, you can buy two off the shelf cables at your favorite parts place and replace them.
Clean the mounting stud on the frame so the threads are shiny, and use a WASHER to get good contact between the stud and the cables, then spray then with a battery terminal spray.

2. Replace your Power cable from the Battery to the Starter and the Alternator, you can buy off the shelf cables that have multiple attachment off shoots and run new power leads to your starter and alternator, probably wouldn't hurt to run new wires to each.

These are the most common points of failure in these older cars, and often over looked, as Oh I changed the end, but it still isn't right.
The Ground wire if still original is a unshielded bare copper braided single wire with a frame attachment point. These bare wires over the years have been subject to road grime battery outgassing and can corrode so that instead of being a big honking wire have become individual single strands of wire.

3. Riddle me this, what to Divorces, Computers, Good Coffee and Electrics all have in common?

THEY ALL START WITH GOOD GROUNDS.
 

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Update: got the alternator to stop squealing, belt was Infact too loose. Now my problem is at the battery it only reads 13.1 volts at idling and 14.5 volts at the alternator idling. Bad ground somewhere? Please help
The circuit between your alternator and battery is bad somewhere.

That can either be on the ground side, or the power side.

The good news is that it is easy to test both sides, even before getting your hands dirty, with a multimeter set to volts.

In this case, I would do a physical inspection of the harness parts and connections, and then follow that with a voltage drop test (read up on it on the internet) on both the ground side loop and the power side loop of the circuit. This is done with the engine and alternator running and connected. More than 2/10ths of the volt drop from one end of the either circuit to the other spells trouble.

The first place I would look would be at the alternator-harness connection. Corrosion here is typical, especially if you have the old molded plugs. The next place I would look would be the neg cable from the battery to the transmission. You have a steel bolt going into an aluminum transmission case. Lovely situation for galvanic corrosion, which also likes to grab your steel so well that your bolt snaps when you try to take it out after 20 years. Plus on FI injection engines you might not have an easy visual on the ground point. Easy to forget to re-connect after a clutch job. Don't forget to look at the battery cable right at the clamp. The cable insulation and clamp can hide corrosion on the copper strands.

Glad you figured out the belt. The extra resistance of the alternator load was enough to make the belt slip.

This can be funny: I recently rebuilt an alternator for a truck. New belt. Thought I had the tension pretty good. Ran fine while idling and for a road test. However, when I took it out at night, and turned on the headlights, I heard a small squeal. I wasn't sure what the noise was at first (hate that feeling), until I turned off the lights and it went away. The extra demand on the alternator from the headlights was just enough to cause the belt to slip.
 

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Discussion Starter #9
Update: just did a voltage drop test on negative side and I got a reading of .15 volts. What's my problem? Thanks
 

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Put on new negative battery cable. Volts went up to 13.7 at the battery. Immediately did a drop test on the negative side. Still reading .45 volts.
 

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You might want to check to see if your alternator has a braided ground strap, and if it does, make sure it is fastened and that the contact area with the holding bolt and engine block are clean of corrosion. That might help your negative numbers. For the whatever holding bolt there is, I would use a new plated bolt or clean-up the old one, and put some anti-seize on it. I think mine attaches to one of the alternator holding bracket bolts. For the loop connector on the braided strap, it should be ok. They coated them with tin so they would not easily corrode.

Look inside your alternator molded plug for any evidence of severe corrosion. That would be lots of green colored junk. They did fill the plugs with helpful sealing paste, which is the brownish stuff, probably a bit dried out after 30+ years. Also check the spades on the alternator for corrosion. They can be cleaned with some small tools, like small files or small caliber rifle brushes.

Replacement plugs which are clamshells that snap together, are available for replacing the molded plugs, if the plug is beyond hope. Get the ones which come with the right angle terminals included. They were used on Lucas alternators. I have seen them on ebay.
 

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Put on new negative battery cable. Volts went up to 13.7 at the battery. Immediately did a drop test on the negative side. Still reading .45 volts.
Both Cables that is Battery to Frame and Frame to the engine/tranny?
 

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Discussion Starter #18
You might want to check to see if your alternator has a braided ground strap, and if it does, make sure it is fastened and that the contact area with the holding bolt and engine block are clean of corrosion. That might help your negative numbers. For the whatever holding bolt there is, I would use a new plated bolt or clean-up the old one, and put some anti-seize on it. I think mine attaches to one of the alternator holding bracket bolts. For the loop connector on the braided strap, it should be ok. They coated them with tin so they would not easily corrode.

Look inside your alternator molded plug for any evidence of severe corrosion. That would be lots of green colored junk. They did fill the plugs with helpful sealing paste, which is the brownish stuff, probably a bit dried out after 30+ years. Also check the spades on the alternator for corrosion. They can be cleaned with some small tools, like small files or small caliber rifle brushes.

Replacement plugs which are clamshells that snap together, are available for replacing the molded plugs, if the plug is beyond hope. Get the ones which come with the right angle terminals included. They were used on Lucas alternators. I have seen them on ebay.
Just did all of this. Cleaned every ground on the chassis. Reading 13.7 volts at the battery. Negative voltage drop test at the alternator read 0.4 volts. Don't know what else to do
 
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