Please lean how to find the info in the manuals. Found below information in less time than it took you to post.

That may be connector C0858 that goes to the Power Transistor that controls the fan speeds below full on..

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FYI, found this image of LR termed Power Transistor that's apparently commonly referred to as a resistor on this side of the pond.
Resistor - Climate Control Blower Motor (Genuine Part # JGN100011 ) - Land Rover connector\relays\flasher from Atlantic British

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yes; that resistor sits inside the blower housing, and if it goes apparently you only have full blowers speed.
I replaced the one on my Mercedes and when it goes that one goes you only get low speed, so there is a very good chance that could be your problem.

 

oh well, regarding the AC and before ordering a new part, decided to pay a visit to the local Junk Yard.
I saw this...

 

and while looking thru it, saw the blower and all the AC under the dash still there.
So I started to "study" and to get familiar with the system.
Based on this unit, the plug I have "hanging" in our Disco goes to the transistor mentioned.
So in order to not leave with empty hands I picked some goodies

 

today I'm playing with ours and trying to fix this issue or at least to trace it down.
Well, it didn't take me long to discover that the PO wasn't very honest about the fact that the AC started to work not in full speed when he disconnected his old stereo system!
How did I came to that conclusion?
take a closer look to where the resistor "supossed to be " if this was an issue related to the audio removal...

 

yep,
that's right....
instead of a resistor I have this....