Starting in 91, a throttle position potentiometer replaced the throttle position switch (actually, two switches).    The earlier "switch" indicated idle or full-throttle positions.  The potentiometer (a continuously variable resistance) shows throttle position throughout the range from idle to full throttle.  This allows boost to be controlled by throttle position, where-as earlier versions with the switches could produce full boost at less than full throttle.  For this reason, earlier versions had to be limited to base boost when Cruise Control was engaged, to avoid uneven operation.  Models with the throttle potentiometer do not have to be limited to base boost when Cruise is engaged.  Also, throttle response is supposedly more natural, although in real life it appears to result in a bit more of a" hunting" feel to the boost pressure at partial throttle sometimes.

91/92 turbo cars (and all later cars, as far as I know) do not have an overboost cutout  switch.  They do, however, have overboost cutout provided by the APC/DI ECU.  When the ECU senses overboost, it cuts off fuel, just as the earlier versions with the overboost switch did.