The other way of running ecu controlled stages of boost is to use the built in PWM circuitry that can be added to every OBD1 USDM ECU. It uses the EGR output at pin A11 to ground the solenoid and effectively switch your boost level.
This is great because it can be used on a strictly by gear basis and can also be activated by an input that is sent to one of the ground inputs of the ecu.
This is how it works, the PWM stands for pulse width modulated but at 100% duty cycle the "pulse" is no longer present and the output turns to grounded output. This means when we want to switch from low to high boost all we need to do is set the PWM output percentage to 100% and it will ground the Solenoid and switch boost levels.
Using this method you do NOT need to use a relay as the ecu is built to handle this type of solenoid. All that is needed is a switched 12v source to one wire of the boost solenoid and the other wire goes to Pin A11 on your OBD1 ecu. It is that simple, just two wires!
Here is an example in NepTune that allows for boost by gear using the dual stage solenoid only when the A/C input is grounded to the ECU. When the A/C input is not grounded the controller is working soley off the first stage.
In the PWM section of NepTune you just need to set it up as follows. Check the enabled PWM box, select a hi/lo input if you wish to do so, select "target boost" from the drop down, and set the frequency to 31hz.
Setting the type to target boost and using a hi/lo boost switch input will allow you to run 0 percent duty to the solenoid in all gears when you want to run "low boost" (off the first stage in every gear).
This section shows you what the target boost setup looks like. You need to set one of the duty cycle levels to 100% and the rest to 0%.
This example shows the solenoid completely off in low boost, this means that it will run off strictly the first stage of the controller in every gear. But when you ground the switch to run high boost it now runs off a boost by gear basis.
In this example it is running off the single stage in 1st and 2nd gear, but in 3rd, 4th, and 5th it is running the higher boost setting. As you can see above the 4psi duty cylcle taget percentage is 0% (first stage only) and the 40psi target percentage is 100% (turns on second stage)
The only other thing you need to do is set all of the IAT PWM corrections to 0. Since you do not want it effecting your duty cycle when switching to 100%.
