Manual or automatic? You can flip a switch to turn on the pump or it can be handled by a sensor. It all depends on how much you want to spend. There are several injection sites that manufacture control boxes. Personally I think that a control box is well worth the money. It will allow you to have more control over when and how much fluid those nozzles will spray.
There are many to choose from. Do your homework and decide which one works best for you.
This site has “Snow Performance” style controllers. Until October 2007, all Labonte MotorSports products have been marketed through Snow Performance. You can now purchase them through the original manufacturer. They also have a controller designed for carbureted engines.
Snow performance does not have a page to purchase a controller separately.
By varying the voltage to the pump you are able to control the water pressure and amount of water going into the intake. This is accomplished by using a controller. I used one by Snow Performance. Like most controllers it requires input from a sensor to control the voltage going to the pump. Lower voltage = less pressure & water.
The Input that this unit was designed for was from the MAF sensor. The voltage output from the MAF is from 0-5v. That voltage is translated to a 0-12v output to the pump. You can set the start and full pressure settings by adjustable dials.
Most sensors send voltage output to the computer in a 1-5v range. For example, at idle the MAF output is 1v. You set the first dial on the controller to start the pump at 3v so that it is not pumping water at idle. The next dial setting is for when you want the full 12v to go to the pump. Set that at 5v when the engine is at full throttle. Everything in between is a smooth linear increase from no spray to full spray.