charging system on 2000 Cadillac Catera

replaced altenator with rebuilt one now won't charge at all. vehicle will not stay running.

Asked by for the 2000 Cadillac Catera
If the battery voltage gets down to around 9 volts or less the car may not run. The electrical system must have 9 volts or more to operate correctly. You probably need to get someone to test the alternator and charging system. You may very well have a new bad alternator
2 answers
The inputs to the alternator should be checked for proper voltage signal. You may need a qualified technician to look at the charging system on your 2000 Cadillac Catera to correctly diagnose your problem.