How do you replas a alltrnater n a 2003 Chevy.

1. Disconnect the negative post of the battery (the positive is easier to get to so you can remove that one instead).
2. Unplug the 3-4 wire harness which plugs into the rear of the alternator.
3. Remove the battery wire (bolted to the rear of the alternator--10mm wrench or socket).
4. Draw a diagram of the serpentine belt routing (you'll have to remove it from the alternator) to ease assembly later on. (There is a diagram provided for you on a little plastic shield above the water pump pulley)
5. Use the belt tensioner to release belt tension so that you can remove the belt from the alternator pulley (only).
6. Remove the alternator mounting bolts (they go through the alternator bracket fromthe front of the engine--which is on the passenger side of the vehicle).
7. To get the alternator out you can either remove both front upper motor mounts and "tilt" the engine forward OR work the alternator forward and then down toward the bottom of the engine (you may have to remove the bracket at the front of the alternator to get more room).
8. Reverse this process to install the alternator.