1992 Cadillac Deville help

Electrical problem
1992 Cadillac Deville V8 Wheel Drive Type unknown Automatic 129, 00 miles

wont hold a charge, battery is good. Dashboard lights flash on and off, blower wont turn off and blows cold air, trouble codes come up, service engine soon, a/c light comes on. It has had front end damage which was repaired, we just tried putting on another ground strap, still no help. Runs great, but wont start again once it is turned off. Mileage is approximate. What do you think it is? Should we clear out the old trouble codes that are stored in the ecm? Or could it be the alternator? We switched the original one with a parts car one.