All motorized ball valves need some type of scheme to reverse the polarity to the motor to cause it to rotate in one direction to open the ball and the other to close it.  Sometimes this scheme is built inside under the motor cover, other times this scheme is external and must be provided for by some outside switch or relay.

With Polarity Reversing valves, two of the three wires leading to the valves have a +/- relationship when the valve is closed and a -/+ relationship when then is valve is to open.  This polarity reversing is handled by a double pole double throw switch or a DPDT relay.

Other ball valves have a relay built inside them or some other arrangement to handle this reversing. With this type of ball valve, one of the three wires is 12V constant power, another constant ground and the third wire acts as a trigger and is 12V when the valve is to open and "float" or ground when it is to close.

Most controller harnesses including Ag Leader's Direct Command will be expecting this type. So the first step is to determine if in fact the Spray Coupe uses the first type (Polarity Reversing).  In my opinion it is likely that it does. Especially since you describe the switches as having a "hot" to the center.

If such is the case, it is possible to rewire the Spray Coupe and utilize a DPDT relay at each of the valves or to swap out the valves for the second type.  You would not use the original switches.

After that, the Ag Leader 10 boom switchbox and Ag Leader wiring can work properly.  This installation is best done by someone who has a through understanding of the Ag Leader system and also the valves.

Due to a routine in the Ag Leader system called "switch presence" and other issues with a Spray Coue, there are many possible areas of confusion. I feel confident that I could make this work but I don't feel confident in attempting to explain all the possible pitfalls.