The oil pressure gage on my 99 Ford explorer is bouncing top to bottom at low idle and occasionally the “Check Gage” light flashes on. There is plenty of oil in it. Does this sound like a sending unit problem or an oil pump problem?
It could be either or neither. (You could have low oil pressure due to internal engine faults other than the oil pump.) It is probably the sender. You can take a chance on this and just replace the sender, or you can get someone to attach (temporarily) a mechanical oil pressure gauge and verify the oil pressure.
It could be a wiring problem or the cluster too. You better get a gauge on it or check the sender with a multimeter.