Still a Work in Progress
Realistically I do not need an intercooler sprayer. I don't track the car or beat on it. I think I only put 400 miles on it last year. But I'm at the point where I'm running out of things to modify on it, and this seemed like a fun project. Plus the 2.5RS has a lot of dummy switch plugs. There are 3 next to the fog light button and 2 on the center console. Having so many blank spots kind of makes the car feel like a base model. The DCCD switches took care of the center console. Now with this modification I'll be able to fill up 2 more spots.
The 2004-2007 USDM sti comes with a very simple Sprayer system. It is a manual momentary switch and a Timer. Meaning you press it and it will spray water on the intercooler for 2 seconds. If you held the butotn in, it would continue spraying until 2 seconds after you release it.The tank is in the trunk and there is a low water sensor that can trigger a light on the gauge cluster. There is no safety built in aside from the light. If you press the button it will run the pump even if the tank is empty. This is what the wiring looks like:
The JDM cars got a more advanced system. In addition to the manual switch they also contained an Auto switch that would communicate with the ECU. The Auto switch will stay depressed and depending on manifold pressure, coolant temp, intake air temp, and RPM; it will automatically spray. If the tank runs out of fluid, it will stop spraying and trigger the same low fluid light on the cluster. This is what the wiring looks like:
Since I have a USDM swap, my ecu doesn't have the ability to output a signal based on MAP, ECT, IAT, and RPM. However I can use a HOBBS switch to trigger AUTO mode based on boost. A HOBBS switch is an pressure switch that show continuity accross both leads at a certain PSI. This is the diagram I mocked up. It's very similar to the JDM design only I replace the ECU with the HOBBS switch. I can also eliminate the DIODE as it was only present to protect the now non-existant ECU:
I wired everything up on the workbench to test the circuit. It works just like it should. However it turns out the low water sensor in the IC tank I have is damaged. I bought another on off eBay so it will be a little while before I circle back to actually doing the install. Here's a video of the wire test explaining everything: