Does your Redhawk include sideview cameras operable with the turn signals? I know the Greyhawks do but I am uncertain whether the Redhawks had them. If yours does include the mirror cameras, do they function?
Does the camera display any picture when you shift into reverse? Or is that when you get "the blue screen"? You mentioned you did disconnect the multiplexer without success. Perhaps you need to determine whether it is receiving power, do you have a multimeter to test for voltage?
There likely is a fuse in the power supply feeding the camera system, perhaps it is blown. I have a Seneca and likely my camera system is different from yours. Mine uses a Voyager switching system and a 3-amp fuse feeds power to the switching module and cameras. The fuse is located very near the module behind the dash.
If you do have a Voyager system I have a connection diagram I could attach.
2014 Seneca 37TS
Toads: 2019 Ford Edge ST or 2013 Ford Focus ST