Hydroxy,
This might work, but you try it at your own risk:
Get a potentiometer, which is nothing more than a variable resistor, and a resistor of equivalent value. So if you get a 5 KOhm potentiometer, then get a 5 KOhm resistor; if you get a 1K pot, then get a 1K resistor. The lower the value of the potentiometer the finer the control you're likely to get.
1. Wire the potentiometer and the resistor IN SERIES. This will create a voltage divider network.
2. Connect the 4 volt source (input voltage) to your voltage divider. For simpicity's sake, connect the positive terminal of your source to the potentiometer side and the negative terminal to the resistor side.
3. For the connection to whatever your destination device is, wire one side to one end of the resistor and the other end to the other end of the resistor. This second point should be where the resistor and potentiometer connect.
Now what you should have is a voltage divider network where the overall resistance of the circuit will change as you turn the potentiometer. Since the potentiometer is nothing more than a variable resistor you will be able to change the voltage going to your destination device.
Here's how it should work. I'll try to make it as clear as I can. Let's say you have a 1K pot and 1K resistor just to make it easy. This gives you a total circuit resistance of 2K (2000) Ohms when the potentiometer is set to it's maximum resistance and only 1K Ohms when the pot is at minimum resistance. This is because when the pot is set to 1K it is added to the resistor's 1K resulting in a total of 2K. When the pot is at minimum it should be at 0K which when added to the 1K resistor results in a total circuit resistance of just 1K.
The key here is that you wire the output of the voltage divider properly. In other words, wherever you need to send this "variable voltage", you need to make sure it's connected only across the resistor and not the entire voltage divider circuit which is the potentiometer and resistor combined.
With 4 Volts coming into the voltage divider circuit:
Scenario A: The potentiometer is set to it's maximum resistance of 1K. Since the pot is at 1K at so is the resistor, the 4 volt input will get divided between the 2 resistances - that means 2 volts across the potentiometer and 2 volts across the resistor. If you wired the output correctly like I mentioned above, the 2 volts across the resistor should go to your destination device (air ride suspension).
Scenario B: The potentiometer is set to it's minimum resistance of 0K. As far as the circuit is concerned there appears to be only one resistance - the 1K resistor. The potentiometer is acting just like bare wire would, almost like it wasn't even there. The entire 4 volts is going across the resistor and will also go the destination device.
Scenario C: The potentiometer is set somewhere between max and min. You'll get some voltage between 2 and 4 volts to the destination device because the 4 volt input is now being split up between the potentiometer and the resistor in direct proportion to their resistances.
I hope this helps and good luck!
