The ignition switch is held in by one (but possible two) very, very small set
screws. If you have the new one in hand, look along the side of it and you'll
find two small holes, 180 degrees apart. These are the holes that the small set
screws fit in. To replace or reattach the switch, remove the speedometer and
use the opening to access and remove the screw on the side of the barrel or to
re-set it. You'll need a small Phillips head screwdriver. Once you remove the
speedometer, you'll see it.
Ted Schumacher helped me with this same project just about a month ago.
Hope this helps.
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