This works perfectly. Thank you so much.
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Call HighLightCells
End Sub
Sub HighLightCells()
ActiveSheet.UsedRange.Cells.FormatConditions.Delete
ActiveSheet.UsedRange.Cells.FormatConditions.Add Type:=xlCellValue, Operator:=xlEqual, _
Formula1:=ActiveCell
ActiveSheet.UsedRange.Cells.FormatConditions(1).Interior.ColorIndex = 4
End Sub