First do this.
This also applies to Discovery with the differences noted.
Switch ignition "off"
Press and hold rear defrost switch then switch on ignition (position 2)-release defroster switch (Note: Release the defroster switch within one second of turning on ignition).
A series of beeps indicates that the MFU is in diagnostic mode.
Perform input checks by operating the following switches/controls. A correct input is indicated with a two beep tone.
Windshield defrost (Classic only)
Rear window defrost
Open and close doors and tailgate
Operate parking/headlamps switch
Wiper switch in intermittent position
Windshield/headlamps wash switch
Rear wiper switch
Drivers seat belt latch
Rear fog lamp switch ('97 Discovery only)
With the system still in diagnostic mode, press and release the rear defroster switch again - now the MFU will provide output signals to the components which will then operate
Rear window defroster and dash indicator lamps
Headlamp wash (not Defender)
Front and rear wipers
Chime and seat belt indicator lamps
Rear fog lamps ('97 Discovery)
Windshield heater ('95 Classic)
This was a bunch of fun, because you can have the headlight washer sqirt 4 second from walking away from the car. We used to "zap" each other all the time...
"Hey,tap the headlight for me, I'm looking for a short....."