1994 Ford Tempo No start/Stall

Recently purchased car. But the battery keeps going down. Battery is the first thought. That only proved a temporary fix. I'm thinking alternter. But before I take that jump I noticed a connector on the back of the intake manifold that was not connected. It's about 1''x 2", grey, going into a black sensor/connector, D/S behind the motor. My question is that could that be rellated. What is it. And could it have been disconnected for a reason. I connected it but the battery had worn down at this time. It will run on ether, but, shuts down after. Any advise would be apreciated.