Cadillac Repair: battery overcharging, cadillac coupe deville, alternator output

Question
I have an 87 Cadillac Coupe DeVille.  The battery was smoking and boiling over by the time I got home.  It has a new alternator and battery is not holding a charge.  The car has not been driven in 3 years since purchase of altenator.  I just bought the car.

Answer
You need to have the alternator tested while it is ON the vehicle as the field wire that causes the aletrnator to charge the battery is controlled by the vehicles computer.

Therefore you can either have an alternator that has a stuck internal regulator and or a faulty computer in the vehicle which is not turning off the signal to the alternator to stop and or limit the alternator output.

If the alternator tests OK when removed from the vehicle and the battery also tests OK when REMOVED from the vehicle and your POSITIVE that bothe battery cables are in good condition as they tend to corrode internally over the years then your problem is in most cases caused by the vehicles computer.