First physical test. The left/right was working, but it was also firing when it shouldn't have been. There were clearly some wrong inputs happening. I don't actually know if the Sears model has the same controller pinout as the INTV 2. There are a few other small questions I'm not sure about, but it's coming along.

Quick update: After discussing some issues at the atariage forums, I realize I need isolation between the console and my power supply so it doesn't damage the console over time. I had assumed I could just keep the voltage low enough, but it might still be a problem. Thus, I need some sort of isolation system. I had considered a more complicated transistor setup or just some solid state relays, but it sounds like optocouplers are going to be the easiest. The only problem with this is the size. I'd need 4 4-channel chips (16 pins each), which is a little ridiculous. I can't find a 4-channel opto-coupler where they all have the same emitter and same cathode, which is what I need. For my application, a 4-channel could be done with 4 anode pins, 1 cathode pin (as ground), 4 collector pins, 1 emitter pin (as ground), and then maybe a power/ground. So 10 pins rather than 16. I can't find a chip with this architecture though, so we may just have half the pins tied together.