Here is a link to some photos of the mid pump controls:
1953 GMC Fire Truck Mid Pump Controls Reference Photos Following the pictures in order I believe the functions of the controls are:
#1 : overview of pump panel
#2 : flow controls for top reels
#3 : flow controls for rear pre-connects
#4 : tank fill valve
#5 : electric reel rewind control
#6 : external connection
#7 : rotary pump flow control
#8 : tank outlet valve
#9 : rotary pressure control
#10: mid pump engagement on dash
