Engine Mechanical problem
1999 Mercury Sable 6 cyl Front Wheel Drive Automatic 136000 miles

I live in WA (state) and in August we had the hotest days every. I drove my car home from work, went back out to start the car and it wouldn't start. It acted like the battery. I replaced the battery, which it needed. Still wouldn't start, I was told to check the starter, the starter was bad, I replaced the starter. And when I tried to start the car, all it does is click. The positive wire got hot to the touch, I replaced it and the starter relay. Now the ground wire gets hot to the touch and still only clicks. I don't know what else to check for. I did crank the engine over manually, and the motor turns manually. What would be causing the starter to just click when I try to start the car.