I am trying to help out a friend who has a older Otis A,B base controller..he needs ro find out what slot the test board safely goes in to the car operation controller.I had the b base years ago but my board slots were xa,xb,etc..and we used the yk slot.his vintage is different it has the slots A thru Z..need to know whicj slot this goes into for troubleshooting..any help appreciated..