2002 monte carlo will not charge has a new battery and a new alternator has 12 volts going to the big post and 12 volt going to 1 of the 2 small wires

Did you check fuses and relays first? Diagnose first, then repair. A new motor comes after you connect 12 volts to the old one and see if it works.

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Fuse Box Diagram Chevrolet Monte Carlo (2000-2005)

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2000, 2001, 2002, 2003 - Here you will find fuse box diagrams of Chevrolet Monte Carlo 2000, 2001, 2002, 2003, 2004 and 2005, get information about the ...

11 1/2 to 12 1/2 is not charging . That's less then battery state of charge , Battery stat of charge should be 12.6 volts , when charging with a volt meter you should see 13.1 to 14.1 volt at the battery posts . Is there a battery symbol lit on your instrument cluster ? Is there battery B+ voltage at the wires hooked to the alternator How to Test an Alternator

Sounds like the alternator if you have replaced the battery. check at the battery posts with a meter when running the vehicle should charge at around 14 volts if you are not getting that with the vehicle running you need to have the alternator checked.

Sounds like alternator if the battery is not staying charged or the output from alternator the big red wire is lost connection to battery +.
a voltmeter you can check with across battery and it should show minimum 13.8 volts minimum to be charging.
if the battery is low it should show 14.7 volts if it shows 12 volts or less with lights heater etc running then alternator is not charging.
You can get a cheap volt ohm meter from radio shack or walmart and use the DC setting 20 volt scale on meter and start the car and turn on everything and put the test leads of meter across battery terminals and see what the voltmeter says.

Sounds like dead battery check battery voltage with a multimeter it should read between 12-12.6 volts anything less than 12 volts you'll need a new battery.

your cranshaft sensor. the car will not start when it's bad. it will crank,but will not start.the altenator is there to supply power to the battery to keep it fully charged with 12 volts.it sounds like your crankshaft sensor is bad. hope this helps.thank you for choosing fixya.com

The gauge could be wrong,it could be defective,have the alternator checked,at the battery,it should read from 13.65 volts to 14.25 volts with the head lights on,and the ac blower on high,with the engine running.If the alternator is new,check for 12 volts at the back of the alternator with engine off,if there is not 12 volts on the large wire,on the alternator,then the circuit is broken somewhere.Just install a new wire,of equal or larger size.Leave the original wire on the alternator,and just add a new wire,larger would be better if possible,and run it from the alternator,to the positive side of the battery,it will fix the problem.

THE ALTERNATOR MOST LIKELY THE PROBLEM, IF THE BATT IS GOOD, THEN IT WILL CHARGE BACK UP WHEN THE CHARGING PROBLEM IS FIXED...HOPE THIS IS SOMEWAY HELPFUL

Charge your battery then have your alternator checked

Then find the problem yourself and fix it. Double check and make sure the battery you have is the correct one for your car . Look at owners manual for the Number of cold cranking amps (CCA) that it requires.Once your sure its the correct battery via CCA and physical size make sure its fully charged.
Mow turn vehicle on and see how its charging. With a voltmeter connected there should be 13.5 to 14.5 volts on that meter with and without accessories on.
Anything lower its under charging anything higher ( waite approx 5minutes after start up before taking to heart meter readings) over charging which is worse.
Check batterry cables and wiring behind alternator for corrosion replace accordingly. If all this checks out do the following:
Remove the negative battery cable from its post and connect an ammeter red probe to the negative battery post and the black probe to the negative battery cable. Now start pulling fuses until the voltage on the meter returns to normal. The fuse you pulled to get this result is the affected circuit. Now you have to probe that circuit from its B+ source to the load
to find the short. Check all connectors for rust and the line for opens or shorting to ground. Repair accordingly. Good luck