Some carts only display in black & white

Hello - I have a 2600A 4-switch "Woody" that I have been fighting with this issue for a month, hoping someone can help steer me in the right direction.

Basically, any cartridge that supports the black & white switch is forced to B&W mode, regardless of the switch position. I have taken apart the switch and checked the contacts, all looks good. I heated up the solder joints on the PCB for the switch, the TIA, and the 6507, no change. I even unseated the TIA and 6507 from their sockets and cleaned the pins & contacts before reinstalling, still no change.

Game carts like Ms Pac Man, where Atari stopped supporting the B&W mode switch, display in color like they are supposed to.

Activision's Starmaster does not switch to the map display when the switch is activated, even if I short the switch posts to closed position for B&W mode.

This issue was present when connected via RF, and has persisted despite modding the unit for component video.

Any advice?