battery charging issues, please help!

I've having some electrical issues with my '92 Jetta. The battery is not charging. The battery is fairly new and the alternator is brand new. Both have been tested. I also replaced a couple grounds under the hood that were in rough shape and added a ground going to the alternator casing, something I've seen recommended on vwvortex.com. Everything else is working properly, I just can't drive for very long without ending up with a dead battery. Any ideas? Also, if I ran a new positive from the alternator directly to the battery, would that bypass the problem and allow the battery to charge? I need to get this fixed in a hurry. Thanks.

 

Sounds like you have a short,or big battery drain.
Hopefully others will weigh in on this.

 

I'm curious what testing method was used; I'm guessing off-vehicle on a bench?

I would check for basic output voltage with it installed. Simply meter either at the battery terminals or directly at the alternator. Should read somewhere in the neighborhood of 13-14 volts. Wondering what you'll get for a reading.

 

It was tested that way at Autozone. I think it read about 14.

 

In order to figure this one out you will need a volt meter. You can buy a cheep one at any auto parts store. You will need to perform some voltage "drop" tests.

In very simple terms resistance in the electrical wires cause a voltage "drop" across the resistance. If there are enough small voltage drops or one large voltage drop between the alternator and the battery then there will not be enough voltage getting to the battery to sufficiently charge it.

The first step is to perform a real time charging test. Simply set the volt meter to DC 20 volts range and place the black lead directly on the negative post (not on the cables but directly on the lead post) of the battery and the red lead directly on the positive post. With the engine running just above idle you should read close to 14 volts. If it is closer to 12 volts then either there is a large voltage drop or the alternator is not working.

The next step is to place the red lead of the volt meter on the output post of the alternator and the black lead of the voltmeter on the positive post of the battery. With the engine running the volt meter should read very close to zero. If it reads one or more volts then you have a voltage drop somewhere between the alternator and the positive battery post. Some likely culprits are corrosion between the positive battery cable end and the battery post and the connection right at the alternator. Simply placing your volt meter leads on the battery post and on the battery cable end very near the post will test the voltage drop there (the reading should be very close to zero). And placing one lead on the alternator post and the cable end that bolts to the alternator will test for voltage drops there. This same process can be use to test the ground side.

If you find voltage drops then you need to repair them.

Me experience with VW's are that there tends to be ground wire issues but also if I am not mistaken if the alternator light in the dash is burned out they will not charge either so do a bulb check by turning the ignition key to the on position and making sure the battery light comes on.

 

Okay, the battery light does not come on. Does that mean the bulb is bad, or could it be something else?

 

If you mean the battery light NEVER comes on, even just when you turn the key on without starting, then yes the bulb is probably burned out.

 

Thanks everyone for all your help (again). Hopefully I can figure this thing out now.