1999 keyless entry pad- intermitant

The driver door keypad on my 99 merc works only sometimes. the dome light inside turns itself on and off at the slightest noise or vibration. I don't even need to touch the door, and the pad and dome light-up.
Do I need a whole new assembly, and if so can anyone spec the part number, serveral are on e-bay , they look like the right part, but all different numbers. Thanks!