what is the small sending unit located near the center front of the engine which uses a single wire that just clips over a straign post?

Trying to determine what part I need to get to fix what appears to be the source of an oil leak.  I just got this little car and can not find a factory service manual yet.  I thought this was the oil sending unit but the replacement sender is like 5 times a big as the unit in the motor.  There is a single yellow wire with a slip on sleeve that clips over the post.  Just below the head and slightly right of center.