Just fixed (in process of fixing) my recently purchased 1994 217S all wheel steer last week. Only front wheel steer was working. Previous owner replaced switch but that wasn’t the problem (I’d check it before changing it, don’t just guess). Front proximity sensor was bad (checked as described in this thread but also disconnected and tested it with 12v applied). Then to be sure, we jumpered it at the connector, and after replacing the fuse we blew messing with it, all wheel steer worked fine. Now awaiting new sensor to arrive but confident it will work. Interestingly, the crab steering still didn’t work, so we eventually checked the solenoid coils on the steering control unit by feeling which ones got warm in different switch positions (but I later read you can just check which ones become magnetized). Comparing what we found with the diagram in the service manual we realized someone had incorrectly swapped two of them. So we switched the two back, and crab steer then worked fine, but one coil was busted (or I broke it during removal) and we’re awaiting a replacement (which BTW we ordered for only $23 using the part number on it, otherwise very difficult to find for our model except through the dealer). I’m a persistent newbie and am just writing this hoping it might help others (as I benefited from reading your earlier posts on this thread).