Just as others have mentioned...big one (circled) is the oil pressure sending unit. Small one is the oil pressure switch. First gens have two instrument clusters. The main cluster has the oil idiot light and if you have a base model that's all you'll have. If you have a nicer model you'll have the separate oil & volt cluster. If you have both these, the idiot light and the pressure gauge, you'll have a separate sending unit for each.