One of my father's computers had one of these.
It literally did nothing except change an LED readout on the case from saying "16" to saying "166".
It literally did nothing except change an LED readout on the case from saying "16" to saying "166".
On the motherboard there was a jumper which took the input from the turbo switch.
To provide feedback to the user, some cases ran a wire from the turbo switch to a bi-color LED on the front of the case as well as to the motherboard to control the turbo state.
On fancier cases they had multiple seven-segment LEDs which had a multi-state jumper for each segment, which decided to light that segment depending if the switch was on or off (example: http://www.minuszerodegrees.net/led_speed_display/LED%20disp...), so you could display either the two different clock frequencies, or a "HI"/"LO" message, or anything you wanted. And connecting that switch input to the motherboard wasn't necessary for the LED to change, so I guess that is how your father's was setup :)