The deal with the switches is a bit weird. All 123, 126, and early 124 models with SLS had a different switch (I'm not sure if the vacuum bleed values are different or not) with different markings instead of the regular 0-3 numerals. Later 124 models had an entirely different switch that was used throughout the 124 range, whether SLS equipped or not. The later switch is preferable because it has check valves integrated into the switch itself and the numbers are on the trimpiece (versus the switch) so they light up at night.
-Aaron
