The cruise control stopped working all the time, then less and less so I replaced the vacuum unit, and fuses, but it still dont work at all. Any ideas? Could it be in the stering column, or a device in the engine compartment? I would assume this is a regular occurance with most units.

You probably have a bad control card sometimes called an amplifier but I think this is a misnomer for it. Replacing this circuit card is what fixed my cruise control. Rebuilt cards are available for about $150. Sometimes you can fix the card by resouldering the component connections on the card but that didn't work for me.
P E H