1999 Ford Mustang Water Damaged Vehicle

I bought a water damaged vehicle and did not know until the next day I had to get a new transmission and engine. I put over 5,000 into this car and wish I would not had paid 5,600 dollars for this car. But since i done already invested so much into its one problem after the next. Something is draining the battery on this car. I bought a brand new battery so its not the battery and all of the ABS/ Service Engine Light/ Brake Lights are staying on/ plus the radiator is brown and we flushed it once but it keeping getting a dirty brown rusty color in it.