Here is the schematic to my 3stage nitrous system I want to build.
It is not 3 systems, but 2 systems controled to act as 3. It is very eletronicly simple and will be cheap to build. It is based on RPM switchs and a hold in circuit.
It is very ajustable and tuneable, with my design I can turn off stages or make them all come on when ever I want. It can do what ever I want, it can go a lot of directions, I could easly replace one or all RPM switches with a time delay.
Basicly how it works is:
You have 2 systems, lets say system A is a plate and system B is a larger shot direct port set up.
The first stage (system A) comes on out of the hole or off the line, it can be RPM triggered no prob, Second stage hapens when (system A) the plate cuts out and the direct ports open up (system B). And to get stage 3 (system A and system B or A+B=3 ), stage 3 could be time delayed or RPM or switch activated, I designed it so it can be changed very easy (before built or after).
This is to help hook a car thats on a big shot and D.O.T. tires.

 

your wiring on the third stage side is very complicated thinking. I did a 5177 kit on a LS1 that had the 2 stage split and made it the with one relay and one rpm activation switch. It worked as 50 full throttle than at 2700 selonoid 1 turned off when #2 came on jetted at 100 then at 4000 rpm Selonoid #1 would come back on and total 150. I also have added single fogger in the belows jetted at 30 wet to add on top of that. If it wasnt auto I wouldnt go more than 2. Just my opionion.