Hey all, I got my first running a-body a few weeks ago. The car has a 225 slant six with factory ac. The previous owner installed an electric fuel pump, new starter, gps, and backup camera(I have since disconnected the gps). The car starts easy when it is cold. The car was missing the dome light bulb. About two weeks ago I installed the dome light bulb. The bulb comes on when the doors open. However, after installing the bulb the car would hardly start and once it started it ran really rough. I removed the bulb and the car was able to start and after a minute or so it ran fine. My initial thought was that the bulb had a short or something and was pulling alot of current(not an electrician). I tested the battery with my multimeter and it checked out(12.5 volts or so). I ended up starting the car and running it without the bulb. I hooked up my multimeter and the battery was around 14 volts. With the car running I put in the bulb and turned all the accessories on(ac, lights, left doors open so bulb is on) and I hooked up my multimeter. The battery voltage slowly dropped until it got to around 12.3 volts and the car started to run rough. I took the bulb back out and again the car ran fine. Today I ran the car with bulb out and turned all the accessories on. The battery voltage was initially around 14 volts but as I let it run it got down to under 13 volts. One site I read told me to test for ac voltage across the terminals to determine if there is a bad diode. I set my multimeter to 200 ac volts and I got around 30 volts ac across the battery terminals. I pulled the alternator and took it to my local auto parts store to have it tested. They tested it three times and said it was good. The alternator that is on the car is a single pulley alternator(I think). I'm not quite sure what to do at this point? I don't know if I should purchase a new alternator? If so should I get another 60 amp alternator or 100 amp alternator? I appreciate any help. Here is a picture of the alternator.