Wondering if anyone recognizes this unused plug under the seat.  Noticed this today, the plug looks clean like everything else in the compartment, for an unused accessory perhaps.  Bike is a 94 K75S without heated grips, the only thin not working on the bike is the low fuel light.

What's the color of the plug, color of the wires, and/or maybe a picture?

Without a picture we can only make wild guesses. If it is in the box with the relays then it could be the accessory plug or the plug for the BMW alarm.

my gut feeling is this is the heated grips plug,this can be used to replace the plug in the fuel tank if needed,it worked for me

Five wires in the back of the plug and one brown (earth) wire waving around free with a spade connector on it is the auxiliary connector. Alternatively, four wires on the plug is the factory fitted alarm and as Stumpy says, can be used to replace the fule tank connector on the early Ks.

Moriarti: heated grips plug is under the left side of the tank .

Sorry Dai, i was sure that was put on my naughty K POST AS A POSSIBLE fault and used the Plug 
conector as described to change into fuel tank connector

Diagnostic Plug - Black 3 pin connector usually with a blue cap

Center hole used for resetting the ABS

Same plug different bike

If it looks like this, it operates the optional mead cooler.

Thanks Dia,  looks as you said,  will sleep well tonight!