Contact reel. Behind the steering wheel - physically it resembles a clockspring, hence the term. Almost always gets damaged if someone replaces a steering shaft u-joint without securing the steering wheel... still you should be able to retrieve a code for it if the sensor unit & wiring was working. As Herb suggests, clean the contacts, and look for that one wire leading up to the instrument panel. Can't recall if it's supposed to carry +12v, or ground (I think it's the former), but when that wire's disconnected the light stays on all the time, it only goes out when the proper signal is supplied by the sender. READ THE FAQS FIRST! A few key warnings and cautions there, to help avoid detonating it in your face... Primarily, disconnect the battery well ahead of time.
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Chris, Dartmouth NS Canada 70 M-B 280SE, 83 245DL, 84 244 turbo, 90 780 turbo, 92 VW Golf, 90 740 Rex/Regina