I think it's time to go back to basics. First, take the battery to a parts store and have them load test it-- it's the best way to know for sure whether it is good-- voltage doesn't give you enough information. Clean the battery posts and make sure it is fully charged.

Move on to the cables. If the negative terminal was bad enough to replace, the whole cable may have corrosion inside. It is worth measuring voltage drops on the cables (a new alternator won't work right if the cables are acting as resistive elements and producing heat). Unbolt and clean all the connection points. Measure the voltage drop on the B+ cable to the fuse box too while you are at it. Sometimes bad cables get hot to the touch when the car is running-- my positive cable was so hot it was hard to touch when it went bad.

With a good battery and proper cabling in place, start the car and measure the alternator output at the big terminal on the back. You want to see 13.7-14.1 VDC (output is temperature and load-dependent). As Klaus mentioned, check the small exciter wire and its connection where it connects to the alternator.

Make sure your serpentine drive belt is in good shape and not slipping. Also, make sure that the alternator light on the dash comes on in key position II-- it's part of the charge circuit.

These problems are frustrating, but the system is relatively simple to diagnose if you are methodical and take measurements at each point. Post back with numbers and people will help.

Good luck!