I have not been on a 4000 in a while, but if I remember correctly it is on the forward engine room bulkhead. If its not there, it could be behind the helm. When you find it, let us know.
This gadget is indeed located on the starboard side of the engine room bulkhead. They probably screwed in the solenoid, then put in the exhaust right in front of it. The fit is so tight that I can't even fit a stubby screw driver in there. On top of the solenoid are fistful of wires all zip tied together and hanging over half of the solenoid. I can barely crawl in that space and can hardly see the solenoid . . . so I couldn't take any photos.
I think what I will have to do is just snip the power as well as the water hoses and just relocate a new solenoid to an accessible spot.
Yes, sometimes that does happen. When the boat was originally assembled, the deck was off the boat and that valve was likely installed from above. Once the deck was on, it is not nearly inaccessible. Unfortunately sometimes items like that are overlooked as to the serviceability. I agree, just cut the wiring and reinstall a new one close by, but in an area where it will be accessible.