If the connector you are talking about has 4 wires in it, it's the control module for the water in fuel sensor circuit. Originally there was an opaque potting material filling the case. By now many have had that material "melt" out. surprisingly most of them still work. Some have tred to replace the goo with other potting materials with varing results. I'm pretty sure they are still available but I think they're kind of pricey.