my volts dropped from 15.5- 11! when i moved car in shop eng,lightandTrans clunk

A computer can be a dead short, being a 95 auto. The cars alt went 20 km and got stopped in the driveway, later on when i started the car to move in the garage, thats when the engine lite came on! after the alt R and R, eng lite went off for two days, then came on! went to dealer for the code to be cleared and problem solved. No i was told the to change trani, cuz of a solenoid, it went on its own power and some poor shifting, but drove in with 15 Volts and drove out 2 days later with 12 Volt. I've kept a charge on the batt, but can't 15 V anymore even when car runs! I think these Auroras need a mechnic who knows these cars. I,m learning the difficulty's and problems of these cars! It's good when the problem is solved in front of the owner, that way you see what a stranger is doing to the classic. The car shore give a good ride and to bad they don't get out enough! WHA, cheers