Is it one of the early EMI-MEC Nichols controls using a Uniselector or a later version with the array of 48v Dc relays replacing the uniselector ??

if I remember correctly the electronic dwell timers us the 2N2046
unijunction transistor

the yellow programing pins have a diode inside
at each step multiple pins can be plugged in to power several relays and solenoid valves
the diodes form a diode "OR" gate to prevent the +48V from one step of uniselector (or later sequencing circuit) back feeding to other step outputs

John