Beyond a backup camera, has anyone hooked up a second camera (or other input source)? Specifically, the 4000. How does switching to that video source work? I suppose this is a question of whether or not it would be pointless to hookup a second, front-facing camera.

It's on the Aux Input; you select it, that comes up.

I Had mine installed so I can park and not hit anything in front of me like concrete deviders.

I Had mine installed so I can park and not hit anything in front of me like concrete deviders.

You've got two options for seeing the camera input, whether you have one camera or two.  You can use aux input and select the camera.  Or, you can hunt down the "camera view" option and turn that on.  Then, it will continually show one of the two camera inputs (there's a button to switch from one to the other).  You tap the screen to go back "into" the stereo, whether source sound control or maps, but after 5 seconds of no tapping it goes back to camera view.   I've got a rear camera that has a split screen mode, where it shows right & left bumper, and I've been using camera view with this mode and it makes for a very nice blind-spot viewer.  I also added "camera view" into my favorites list, so it's a little easier to turn on and off.

I too was having this issue, another thread addresses this issue. For the rear camera, if the reverse wire is hooked up correctly, in my case the camera hot wire hooks up to reverse lamp wire in rear, there is a wire that is in the camera harness that comes out with the rca plug that goes into the head unit, i hooked it up to the reverse wire from the head unit, and enabled the rear view camera, but turned it off, not on. Now when i put it in reverse, the camera comes on and screen works, put in drive, and camera goes off and back to receiver screen. Does not have to be turned off. Now i am going to hook up sony mini-camcorder to aux video and see what happens. If it works nice, i may just order a cheap front camera just for grins. 

That's exactly what I do, just push the aux button. The only drawback is you lose audio but better that then scraping my truck while trying to park.

i purchased a front view camera, hooked up to aux and to my surprise, the image was reversed and had assist lines. Needless to say i was not happy. I contacted amazon seller, and they said it was Amazon fault. Amazon immediately credited my card, and sent me prepaid return label. I ordered a second front view camera, and waiting for it. 

i purchased a front view camera, hooked up to aux and to my surprise, the image was reversed and had assist lines. Needless to say i was not happy. I contacted amazon seller, and they said it was Amazon fault. Amazon immediately credited my card, and sent me prepaid return label. I ordered a second front view camera, and waiting for it. 

some cameras come with a blue and white wire that are looped. One is for the reverse image and for the parking guides. Just needs to be clipped and image will be reversed and no guidelines

My rear camera does have the two wires, but the supposedly front camera does not have them. I wish it did, problem would be resolved. 

Second front view camera arrived, wrong one again, from a different supplier on amazon. Just returned them both and ordered a boyo digital tv tuner instead. figured i will never use front camera anyway.