Techno Stuff
How They Work - Index Units

Indexing a ratchet is a little different, as there is not really a home position for the ratchet. In this case, all the index unit is doing is stopping the ratchet from turning. As usual, sometimes the default state of the unit is to stop the rotation (e.g. spotting index unit keeps spotting wipers from turning most of the time). Sometimes the default state is to let the unit turn, which is the case for the search index unit below.

miscellaeous parts
search ratchet not indexed

In this pic, we are looking at the control unit from the motor end, and the search index contact plate is removed, so we can see the wipers. The picture is rotated 90 degrees. The search index unit in it's inactive state allows the search ratchet and wipers to turn.

miscellaeous parts
search index unit active

OK, here we have detected a winner and payout is supposed to happen, so the search index coil is turned on and the arm is engaged in a tooth on the ratchet, stopping it from turning. As you can probably guess by the shape of the teeth on the ratchet, the ratchet is rotating counter-clockwise when viewed from this end of the control unit shaft.