http://www.ebay.com/itm/190570447682

AM tuner cartridge, for use in the Toshiba RT-K2 walkman.

now that i have seen the otherside of this, via the ebay page, and seeing the "pins' needed for power - ( I guess ) and maybe signal or - other accessing the 'host' player for - more circuitry - that this will NOT work in anything else but a Toshiba RT-K2 walkman, Correct ?

Yes.  The player might also have a cutout in the cassette door window to tune the channel.  Not sure.  There were 3 such tuners available and this is the rarest of the 3, different colors, and I think this model is the only only red one.

The RP-A2 red Am tuner module has identical 6 pins that the RP-S2 FM tuner has.  These two tuners will work in the KT-S1, KT-S2, KT-S3, KT-S4 and also the earlier KT-R1 and KT-R2 recording models (one of largest walkman made).   All these models have the cutout area in the clear part of door for tuning dial to be adjusted.  The Toshiba tuners came in Blue, Red, Black and Silver.   You are correct on rarity the AM red RP-A2 is by far the rarest but of little desire as who listened to AM but sports and  news people.  I was lucky to get mine with the original red box ( One of reasons so rare is they did NOT to my knowledge come with the walkman when you purchased it.  Only the FM tuner module came with player you had to buy the AM tuner as a separate accessory.  Tuner modules are all generally rare as over decades the tuner that looks like a cassette gets misplaced or lost or separated from the player.  I have over 30 players all with their tuner modules a specialty area of collecting for me.

  Here is a link to a old post of mine showing all but one of the entire 8 model range of Toshiba tuner modules.

index.php?board_oid=193392314111653483&content_oid=193392314112137437

Here is picture of both the KT-R1 and R2 with my NIB RP-A2 Am tuner and the RP-S2 FM tuner.  Also have the original demonstration tapes for these models

But some fool did delete my kts1 topic and the other one also