Because this can probably explain it better than I
http://http://www.alcohol-injection.com/instructions/stage%201%20water%20injection%2001.pdf That is the pdf install instructions, the relay in question is on page 11. Btw the pages aren't in a normal order due to the way they scanned it in so you have to look at page number. Makes it fun to work with.......
Also if you are curious about how I am installing it
http://http://www.ozmpsclub.com/forum/intake-exhaust-turbos/6218-meth-h20-injection.html
I would prefer not having to go into the passenger area because the entire rest of the install is in the engine bay at the front.
Also by the way, rob82 I assume they meant to go off of the 12 v signal side of the injector relay not the potentially high voltage high current side. No matter what the injectors do they shouldn't have any impact on the signal side of the relay. I'm also quite interested in this injector stuff because if I get a wotbox installed I would end up with a point of high boost (so the meth system is being injected) but no ignition during gear changes so it would probably be a good idea that meth shut down for this to prevent any chance of it flooding the engine.