05 Pontiac Aztek charging battery to above 19 volts!!!???

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pappaanimal

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I have a 2005 Pontiac Aztec with 240,000 miles. I changed the water pump, lower radiator hose, spark plugs, spark plug wires, and alternator. I topped off the fluids and started the car so I could vent air out of the coolant system. About 2 minutes after starting the car the battery starting bubbling and then exploded spraying acid everywhere. The battery is only 2 weeks old but I thought it may have a bad cell causing the voltage to spike. Walmart replaced the battery under warranty. I installed the new battery and it also started the bubble before I got the car turned off. I checked the battery with a multimeter and it reads 12.78 volts with the car turned off. When the car is started it rises almost immediately to 17.5 volts and then continues to raise well above 19.5 volts. I pulled the alternator, thinking it is bad straight out of the box. I had it tested and it tested good at the auto parts store. What is going on here?:confused: Any help would be appreciated as it is difficult to change out the alternator on the car and I would like to solve the problem before I bolt everything back in place. Thanks in advance.
 
the wire lead going to the voltage regulator in the alternator probably has a break usually at the connector. With the engine off take a voltage reading at each of the two wires on the double wire connector, you should get full battery voltage on the thicker wire and a lower reading on the thinner wire.
 
There is only one wire at the connector. It is a four pin connector but there is only one wire from the connector back to the cable run. Looking at the connector it only ever had one wire. There is no pins in any of the other slots and the other three sluts are plugged. The only other wire is a thick one that bolts on to the side of the alternator.
 
The connector on the alt only has one wire. The other three holes on the connector are plugged. It looks like they never had a wire run to them. The one wire runs back to the cable run. There is one thick red wire that is bolted to the case on the alt. Those are the only two wires. Are these the two wires you are talking about?
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you have a one wire set up to the regulator. The post that is marked B+ should have battery voltage, what does the other wire have voltage wise?
 
The connector has 0 volts. I found a break in the wire but it also has 0 volts. I soldered in a new price of wire anyway. I still have 0 volts at the connector.
 
which connector?
 
The four pin connector that has one wire. Are you asking me to check the voltage at the pin on the back of the alternator?
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OK so I went ahead and bolted everything back together and decided to try it. The battery voltage came up to 14.69 volts and held steady. Thank you so much for your help. I would never have thought to look for a broken wire. Thanks a bunch!
 
excellant, that broken wire is the feed for the voltage regulator and without any return voltage the regulator goes to full output.
 
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