Ok, so I wired it exactly as shown on the schematic I attached in my post. The TX LED (connected to TX on the CH340G and RX on the 644P) stays on very dim, and occasionally flickers between different levels of brightness, which I assume isn't supposed to happen. I think maybe my board's power supply is flaky? The RX LED stays off. Whenever I send something over the serial monitor, the TX LED flickers when I hit enter but the RX LED still stays off. Again, my TX LED is connected to TX on the CH340G, not the 644P. Maybe I'm calling it opposites. I'm confused lol