Sharing controls with one encoder and another encoder just not at the same time.

[Vocalitus]

Yes I know we have been here before and the answer was a USB switch box but it is a bit more complicated than that, and I am sure it can be done.

Quite simply I have a 2 player control panel.  One side (Player 1) is for original Xbox with Kade (which works fine) sharing Joystick two for games like Robotron (which works fine) and two buttons for Coin and Player start.

Introduce the Pi/PC and use the EG Starts encoder for either platform with an USB switch box (currently Pi) using the Player 2 side and not bothering with Player 1 Joystick.  The Pi is for Light gun and mouse/spinner games.  That works fine until about 2 hours ago and now both sides do not work.  The Kade is mounted above the control panel as there is not enough room and all the wiring reaches without strain.

The only thing I think I know where I am going wrong, is I'm using a global grounding wire between both encoders.  Ground is ground right?  And the ground is going to earth on the power plug.  The switches are not taking power from either controller.  I disable the Pi and nothing changes.  Both the EG and KADE are showing green across the board and by all accounts are working fine, except the buttons do not light up on the Pi side.  Everything is powered separately so it is not an USB amperage issue. The xbox did go into Error code 19 but after some violent shaking it now boots. 

Only Player one (Kade) is sharing a joystick and two buttons.  Player two is sharing the same two buttons. 

What am I doing wrong?   

[Vocalitus]

Well I figured it out.  I used 5 diodes to the shared joystick to both encoders and it works.

I was wiring my backup car camera and I wanted to use it in case I had people too close to me at the drive thru.  Using diodes I could isolate the reverse light from coming on when I flicked the switch even though it solved the tailgating problem I was having but could cause accidents down the road. 

So I had a moment of clarity and solved my arcade problem.  Simples.