Sweet.
If the cable works this way, you can probably leave it and be fine. But DeOxit the cable and cable connectors. I don't know if some of the cables are directional or not, as I've never troubleshot it further. But I have seen some work in one direction but not both, where others work in both. I'll have to look into that one the next time I see it.
The cables on these are just SCSI disk drive cables, you can buy new ones on ebay. Search for '24" 3-device 50-pin SCSI cable'. I've bought these exact ones from this seller:
Color: Grey Cable, Black Connectors CablesOnline Part Number: FS-002. Great for your 50 pin narrow SCSI machine. Flat cables can help with ventilation especially in tight quarters. []---------- 16"---------- []---- 8"---- [].
www.ebay.com
The only catch is on some of them you have to grind the key tab off of the cable connectors, if the connectors on your game boards don't have the key slot. (But that's easy to do with an exacto or file.) I think some boardsets have the key slots and others don't. (And a lot of them just have the connector housings partly broken off.)
Also, each of the self-tests is useful. Get to know them. The most useful is the one with the ROM self-tests, as it also tests the coprocessor board, and the video RAM, and it has indicators for all of the inputs, all on that one screen. (Each of the 'dots' on the right side of the screen turns to an asterisk when you close the input switch or button it corresponds to.) But each of the other self-tests does other useful stuff too.
These boardsets are pretty interesting hardware, between what's on all 3 boards. It's a little strange that for such a simple game, the hardware has a lot going on. (Probably because it's just inefficiently designed.) Aside from the 4-channel audio, the game is basically Pac Man, which runs on a single simple board. But they're fun to work on.
I just picked up a Nato Defense boardset on ebay for $80. Complete and all original, even the paper stickers are untouched. Nato Defense uses the same three boards as Thief, but they are heavily modified for ND, with a lot of blue wire mods. (And the ROMs are different, and there are more of them.) I've never repaired a set though, so I'm looking forward to digging into them.