sending unit wire?

[kevoinc]

I changed the Cat and the plugs the other day on my 89,it was pretty easy except for the last one which was the front plug on the passenger side.Here is my question,there looks to be a sending unit between the front 2 plugs on the drivers side.The wire broke off of it when i was changing them.Does anybody know what this is?The car runs fine,no codes,all readouts from the dash are normal.Any help will be appreciated.