Since the purpose the "yellow wire" is to drive a relay, as Adriatic suggests you can skip the middle-man and go directly to a circuit that drives a relay. If not comfortable with component-level assembly, Azatrax sells off-the-shelf latching relay modules. Here's one with screw-terminals that might not require any soldering. Apparently there have been different style of Marx switches, but here's how I figure it would be applied to the most common switch-controller configuration (3 wires between the switch and the controller).
