Thanks, jshadows and Brandon. I ended up making a spanner wrench out of a flathead screwdriver. I figured the plastic surrounding nut would crumble. Both wires were intact and I cleaned all contacts.

Anybody doing this for the first time....the tube has a notch and the top-plate has a long ridge - they must line up for a good seat.

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1983 300SD 307k miles
1993 Ford Escort Wagon 215k miles
1995 Isuzu P'up 214k miles