Pump in the area behind the starboard cup holder. Module in the starboard storage area above the rear u shaped couch in the aft area. Short runs to the helm for wires and pump lines. Also installed the rudder sensor. I also have an auto pilot.
More than likely you cannot open the seacock because it is locked. It is illegal to dump into local waters, so your seacock has a lock on it to show that it is closed in case you are boarded by the authorities.
You might need to replace the manifold. That's what finally happened on mine. It was doing thw same thing, cutting aout after 20 minutes. You can try flushing by taking off the raw water intake hose and the discharge hose and flushing by pumping something like barnacle buster through the...