1999 cadillac catera won't start (battery ok). my engine light stays on and there is sometimes a clicking sound from the steering wheel column. any suggestions?

There are two universal joints between the steering wheel and steering gear. Could be one or both.

Well here's your steering column. My best guess parts 16-20

starter?
New battery drained = something is still powered, open/short.
new ign switch and steering won't lock = something was not put together right and the ignition is staying on and draining the battery.

First have your alternator checked to see if the diode or regulator are getting weak. When they do that also have the battery tested for a dead cell. If after preforming these two test and nothing is found to be wrong, then it is most likely a computer error. when was the last time you had all the computer codings read and reset? If it's been awhile a good decoding cleanup my be the answer.

fly wheel bolts tight?

have you refitted the transponder from the original steering coloumn ,then it will start

Check that the fuel pump is working. Take th egas cap off and have some-one turn on the ignition to run. If you hear a light motor sound it should be OK.
If not, you need to make sure you are using the right key for the car. The key is coded and if it is not the correct key, the engine will crank but the fule will be cut off via the pump.

Check the fuses (under the steering column behind panel) for a fuel pump circuit. I beleive there is fuel pump relay which needs to be checked.

What is the question?

The fuse box is under the steering column, behind a panel where your knees are.
More fuses next to battery.

There are 2 screws which hold the large panel right under the steering column. They use a large flat head screwdriver and are 1/4 turn. They are right on the bottom edge of this padded panel. The panel, which your knees should almost touch when sitting in the driver's seat, needs to be lifted up (slide it) after removing the screws as it is keyhole pinned.
The fuses are under there....there are more next to the battery as well.

Sounds like a steering column that is not grounded or if that is ok then you have a recall for the steering clockspring as for the battery light check your charging system