Low voltage does all sorts of strange things in the W126. Did your wipers start up too? This has been known to happen. The cruise will not work properly at low voltage, the gauges will go nuts, and the compressor will drop off line, ditto for the climate control -- it defaults to full heat defrost.
Get the battery checked, it may have a bad cell so the voltage drops. Get the alternator checked too, you may have blown a diode.
Check your fuses too, in case something got hot and melted, shorting things out.
Could also be a fried ignition switch, completely unrelated to the rear seat adjustments
My brother didn't show the kids the rear seat adjuster on purpose.......
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!