Need Help! Car Turns off when in park.

Try cleaning the throttle body and perhaps the IAC (Idle Air Control) solenoid. They get gooped up over time and can't compensate for differences in engine load (or no load) quickly. As for the lights dimming - If the Alternator wasn't working, your lights would always be dim and eventually, you couldn't start the car. Now for the shaking you describe: sounds like an engine miss. Sounds like your car may not have had any maintenance done in a long time. Typically, the spark plug wires deteriorate and cause misfires by allowing spark to jump to ground rather than through the spark plugs.