I have recently acquired a 2003 Cadillac CTS Automatic, I am borrowing it for a few months until I deploy. (I sold my truck). Take into note, the vehicle has been sitting in a garage for nearly 2 years. Only drove 2 times in that 2 years. The first thing I did was buy and install a BRAND NEW battery. As soon as the b atterry was placed and connected all of the electronics, headlights, air conditioning kicked on. I went to start the vehicle and nothing happened. Did not even try to click or turn over. Well I wiggled the ground cable on the battery and I'm not sure what you call it, but I heard a, I guess you could call it a whining noise and some corresponding clicks. I immediately tightened the ground cable and went back into the vehicle and it turned over.

Well it ran great all day, I took it to Wal-Mart. Parked it and went inside to pay for an oil change. After the oil change I drove to my house and parked the vehicle. The next day around 1500 I went out to start the vehicle and the same thing happened. I turned the key to the ON position, all the electronics, navigation, air, all kicked on but when I went to start it, it did nothing. No clicks, not even an attempt at rolling over. I thought that maybe the batterry had somehow died so I tried to jump it with my wife's vehicle, but it still did the same thing.

The next day my dad came over, he is the owner of the vehicle. The battery was dead, being that for some reason it does not let me take the key out when the vehicle fails to start. We even tested the battery and it confirmed it was dead, so we hooked it up to his truck to try and jump it. The instant we hooked the cables up the Cadillac lit up, I heard the same whining noise, all the clicking sounds, I jumped in the vehicle and it started. We took it to walmart and asked them to check it out for us. By the end of it they ended up changing the bolt that connects the ground to the battery. The Cadillac started, I drove it home, parked it. About an hour later I came out to go to work, it started right back up. I drove it to work, parked it, it sat for 16 hours (I work in the oil field). I got back to the car after a night of work, got in it and it started right up. Drove it home, parked it, went to bed, woke up 5 hours later for work and when I went to get in the Cadillac, the same issue occurred. Electronics fire, but when I turn the key everything goes black, no crank, nothing.

The next day I changed out the entire ground cable at my house, it started right up. I left it running for a bit, came out, turned it off, started it again to make sure it worked. Did this 3 times and all three times it cranked over perfectly. I turned it off, about an hour later came out to start it and the same issue occurred. I have checked the relay, even swapped it for a similar relay. Did not help. I have repositioned the cable and it has worked, I here the whining sound, all the clicking. I hump in it starts up, I test it a few times, it works. I leave it for an hour come back and the same issue happens.

I have a SnapOn test light and I am getting power to all the relays. The weird thing that I cant figure out is that when I have the test light grounded and I test what I believe is the starter ignition wire? I believe its yellow, I can get it to crank but not start.

Well believe it or not last night I had the same issue, pulled out the test light, put it on the yellow wire that is in a harness on the fuse box, the one that I believe has something to do with the starter, and it fired right up.... The damn key wasn't even all the way in the ON Position. I let the car run for a bit. Shut it off, started it a couple times, no issues. Went to bed around 0630 woke up for work and again had the same issue. I plopped the hood took the test wire to the yellow wire again and it fired up.

On my way to work NOW it is having shifting issues. Extremely hard down shifts, when shifting up it is pulling more than it was before when I had drove it.

So now I am coming here for help, I have NO clue where to even begin, I can do all the work myself. I just need to know exactly what's wrong and what parts may need to be tested or replaced.