key on no power at all

Check for blown fuses.

Also double check the battery connections old connections sometimes don't tighten all the way down and need to be replaced.

Verify power at every point from the battery to the starter relay. If all points verify 12 volts, then replace your ignition switch. ALL PRE 1990 LINCOLN MARK VIIS SHOULD HAVE THEIR FACTORY IGNITION SWITCHES REPLACED http://www.thelincolnmarkviiclub.org/documents/tech/1984ignitionSwitch.pdf

Thanks very much oldschool that's what I was thinking myself.