I am not sure whether this is of any help but there is a cautionary note with an explanation already in the technical manual (but I don't know how to interpret this):
Note: The description "Idle Increase Solenoid" for item 51 on "280SL (US Version) Wiring Diagram" is incorrect. The idle increase soleniod is uni-directional (extended when energized, spring return), whereas the solenoid on the schematic is bi-directional. What is shown appears to be the transmission solenoid which is three position with two coils, extended, mid positon, and retracted. The wiring indicates extended positon when the "venturi control switch" is closed, and retracted position when the "kick down switch" is closed, which is the function of the transmission solenoid. The "Idle Solenoid" does not appear on this schematic, nor do the forward and reverse auto-transmission pressure switches.
Also the wiring colors from the double-lift-solenoid [or double-acting-solenoid] are brown-yellow-and black, where the two brown wires end in a single larger terminal connector than the other two.
How they are connected to the terminal strip is mentioned on page 27-26/7 in the BBB - see attached photo.