Need advice for making a NES-SNES-N64 system

[off]

Hello, im making a NES-SNES-N64-in-one-console.
Since I am not very skilled with electronics Im keeping it simple with two adapters. And a switch or two to change system. I probably have that part figgured out. But I need some advice how to connect the audio/video signals to one outlet.

The idea is to use composite signals from all systems. Please tell me if it will work:


NES only has mono audio but I can just connect it to both audio outlets, right?
The idea with the diodes is to prevent electricity going into the PCBs for the two units not beeing used, at least prevent one direction since I have to connect the ground as well.
Do I need the diodes at all? If I do what type of voltage/amp should they have?
Can I connect ground to only one of the PCB, or do I need all three?

Is there a better way to do it? Keeping in mind it has to be easy.
Please tell me if you know of a multi console system tutorial, that could help.

[Grambo]

Please tell me if it will work:

No, it will not.

Is there a better way to do it?

Yes. Lots.

http://www.ebay.com/itm/3-Video-Devices-to-1-Composite-AV-Signal-Switch-w-RCA-AV-cable-TV-Set-/300964338720?pt=US_Video_Cables_Adapters&hash=item4612df5c20

5 bucks.

*edit*
Oh, and this:

http://www.ebay.com/itm/RCA-Male-Plug-to-2-RCA-Female-Jack-Y-Splitter-Audio-Video-AV-Adapter-Cable-B-S5-/281199478304?pt=US_Audio_Cables_Adapters&hash=item4178cb8620

[off]

You are right.
Dont like the switch however, but now im thinking I should replace the diodes with relays. More complex but im making an attempt.
Problem is powering all three systems. I was hoping to use the N64 adapter for all systems but the 12V 0,8A is probably not sufficient for the SNES. 
So I guess two adapters (another switch) needed now.

[Grambo]

Please do keep me updated with your progress.

[ApolloBoy]

You are right.
Dont like the switch however, but now im thinking I should replace the diodes with relays. More complex but im making an attempt.
Problem is powering all three systems. I was hoping to use the N64 adapter for all systems but the 12V 0,8A is probably not sufficient for the SNES. 
So I guess two adapters (another switch) needed now.

The SNES should be just fine with 800 mA, it doesn't really draw that much power.

[off]

There are different SNES vertions. Im in europe, so im refering to a PAL sytem and then there is the one and two ship vertion of those.
Will do a little test before i build it. Whats a good spot on the board to test the draw?