Firstly let me apologise as I suspect all of below has been covered in this excellent forum.
Just bought a '97 300tdi auto which I am very pleased with as it has little corrosion due to spending the first 10 years of it's life overseas (think in Japan).
My first question is regarding the MFU as I have no interior lights at all (front, middle or rear) and wondered if the MFU can cause individual systems to fail. Checked bulbs and connections etc. which are all fine and also know that the door switch is fine as I get a chime when I open the door with the lights on.
Heated rear window, fog lights, intermittent wipers, headlight washers all work absolutely fine, rear wiper is intermittent and rear wash as a pump or pipe blockage.
Secondly, am I correct in saying that appears to be no permanent live feed to the stereo? It has an aftermarket unit fitted but loses the memory once switched off because of this. I can take a feed off the clock or hazard light switch easily if this is the case?
Lastly, if when the aircon is switched on and there is no light on the switch but the engine speed increases and fan engages, does this indicate that the system is not pressurised?
Thanks and look forward to the replies.
By the way the last Land Rover I had was a Series 3 lightweight that I put a P6 V8 engine in, that was over 30 years ago, how time flies!

I've attached two drawings from RAVE which shows that the lack of internal lights and the permanent supply to the radio might just be down to a blown fuse, but yes, the interior lights and the radio memory are, or should be on the same circuit.
The drawings also show you that the MFU supplies the switched ground volts to bring the lights on when the doors open, the MFU is between the doors and the lights. The individual switches on each light is switching a ground connection.
Regarding your A/C problem, sorry, I can't help with that.

You should find a purple wire in a head unit connector in the dash behind the head unit that's live, the switch live is green/orange.

Switching on the AC will raise the engine revs slightly to compensate for the additional load placed on the engine, the twin cooling fans behind the grill and in front of the condenser will also run as soon as AC it's switch on.
You may have a blown bulb in the AC switch also if your getting very cold air blowing into the cab then the system is ok but there nothing to stop u getting the refrigerant level checked.

Thank you both.
There was indeed a 20 amp fuse that was blown, bizarrely in the workshop manual this shows as 'trailer lights', which is confusing.
I now have partial interior lights (front not working, yet), plus a clock that appears to work consistently.
Regarding the AC, it's too cold at the minute for it to kick-in, it would be great if it did work though.
Just need to try and figure why the cruise control is not working now, replaced all the perished hoses with silicone but still no joy. Need to test pump etc.

Which workshop manual states that ? As LRs electrical manual states trailer aux socket, Haynes just as trailer socket, I use this feed to power my fridge in the boot via aux socket.

AC should cut-in any time what ever the outside temps maybe,I have mine switch on most times summer or winter.
Cruise control could be a problem hose with you have replaced then there's actuator diaphragm, pedal switches and the pump, fortunately there is a diagnostic/electrical test function on the ECU that u can do with a multimeter, I have a copy saved somewhere I'll see if I can find it, also it's in the Forum somewhere.

This is stated in a genuine workshop manual from 1995 on?
I thought AC only worked in temperatures above about 4 or 5 degrees C?
Regarding the cruise control, all hoses now fine, have checked actuator diaphragm by sucking on new pipe, so need to check pedal switch, pump and ecu presumably? Do you know if pump runs when car idling and in drive and cruise switched on?

The vehicle needs to be doing a minimum of 28-30mph before the pump cuts in.
AC is handy to reducing humidity when in the cab in winter and if your covered in snow and the cab is missing up, just switch air recirculation on and blower on full and things are toasty in minutes, assuming the engine is hot that is.

I see that the owners handbook states 20 amp fuse for "trailer lights" so that's incorrect.