96 seville sls electrical gremlin!!!

I bought this car a few weeks ago and fell in love..however some electrical problems have arose that are making me wonder why.First off when I bought the car the indicator light for the left turn signal was steadily on,I changed the bulb in the front that is the turn signal and parking lite and the parking lite does not work.The next problem was the radio stopped working when i tryed to use the cd changer in the trunk and then a day later the car would start and then stall.I took it to the dealer and they reset the codes and tighted up the batterys positive terminal and that fixed it for a while.After that i was having intermitted electric window problems..sometimes they quit working and then a few hours or days(depending on mood of car LOL)it would work again.Now my biggest problem is that my mother in law got in the car and pushed some buttons on the ac and that quit working.Compressor will not come on and it is displaying on the info screen very low refriderant ac comp not on..Please help me....

bottom line all electrical problems with northstars start when u dont use the proper harness for the radio pull the radio out make sure its not joyriged
99 percernt of the time its right there