Heater & cruis cont. Work and don't work at same times. When not working if fan speed selector is in off or high cruise light comes on. And now low oil light is intermitent.

Those are normally unrelated systems and circuits but I'm suspecting a common ground problem could be causing these symptoms.
You may as well start at the battery cables. Check both ends of both battery cable to make certain that both ends of both cables are clean and tight, free from corrosion, etc. You want to be sure of a good, solid connection.
If those check out good, you'll have to check the individual grounds for each system. Those ground points will be harder to access since they will be in various locations on the vehicle.
Let us know if you need a little more help.