P38A P38 heater duct problem

Hi
Year 2000 P38 T/Diesel. I am trying to renew the O rings behind the dash as they have been leaking for some time. Many thanks for all the advice on the Forum about the way to do this.
However I have one query concerning the duct which goes across from the heater motor to the dash right side face vent. This is the duct behind the instrument panel.
There is a small (approx 40mm x 40mm x 10mm) black square "thing" fixed to the top of the duct with a single wire coming from it. It is fixed about half way along. I will try to attach a photo to this thread. I assume that it is some type of heat sensor ???
However the wire coming from it has been cut off about 6" away from the square "thing". I know that I did not cut it off so presumably someone has been in there before me and sliced through the wire. It is an old cut ie does not glisten as if newly cut.
I cannot find the other end of this cut wire.
Does it do anything ? Should I try to reattach the wire. But to what ?
Any help appreciated.
Many thanks.

It may be part of a tracking device, fitted when it was worth nicking. Just a guess by the way.

Looks like its stuck on with a sticky pad, so I am with Alan, part of alarm tracker system.

Its a gps antenna from an old tracker as said or maybe an aftermarket sat nav,

That is really helpful of you all to reply and puts my mind at rest I think ! I really couldnt think what it might be. I felt fairly certain that I had not cut the wire.but couldnt be 100% certain !
It certainly looks as if it is stuck on with a sticky pad.
Wow. The power of the Forum !
Many, many thanks for the replies. Now I can get on with the horrible job of replacing the O rings !