When look at a component in the electrical cabinet or wire, the number indicates what page in the schematics that the component can be found at. For example, 6U1 is the hoist inverter (VFD) found on page 6. Wire #1503 is found on page 15 and is wire# 03 in a sequence.
S=Hoist (pg 6)
R=Slew (swing) (pg 9)
C=Trolley (pg 12)
F=BrakeKL= Safety validation for the drives