Several posibilities:

First, the bushings in the shift linkage fall out with age on these cars, helped no doubt by the temperatures (I used to live in Sault Ste. Maire, I know). When they are missing, the lever may not push far enough to engage the safety switch in Park, although you can get it to work in Neutral. May have to move shift lever around while holding the key over in the start position to find where it works.

Second, the switch itself may be bad, or the wiring loose.

Third, the solenoid on the starter is bad, or the wiring is bad, so that no current it being applied to the solenoid, hence no start. The safety switch is in the circuit.

And don't forget that ignition switches go bad, too -- if the switch is worn out or loose, it may not make contact.

You can check these things with a voltmeter or a test lamp, but not outside in the middle of the winter! You must get 12V at the small wire on the starter (driver's side) with the key in start position. If not, trace back to the safety switch and see if the juice is getting there. Check for continuity across the safety switch in neutral and park, etc.

If you hear a loud click and the lights dim or go out, the starter is shot. They wear out and lock up, both of ours have.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!