Welcome back, My 1987 mercury grand marquis gs sedan is going nuts. When I have the key on OFF all of the lights will come on the dash but when I turn the key to on and/or start it will lose all power and won't start. please help.

 

This does go back a bit, but if I remember correctly, when you turn the key on and to the start position the ign tumbler is meshed with a rack that as a rod that goes down to the ign sw assy lower down on the steering col near the brake pedal area. From what you describe it sounds like there is either a problem with the switch down on the column or the rack coming from the upper part of the steering col. Some of those switches were adjustable and if the linkage was working correctly , you could adjust the position of the switch for proper function.