I realise this is over a month old - but I had exactly the same last week on a trip to France.
Check fuse F15. On a facelift at least, if it blows, you lose speedo, rev counter, fuel gauge and engine temp on the dash. You also lose most trip computer functions. The dash remains illuminated (if the lights are on) and the car runs normally.
My fuse F15 had blown. I replaced F15 with the horn fuse (F17) but that blew again within half an hour. I replaced it again, and it blew a few seconds after ignition on. I then spent an hour or so pouring over the Haynes manual, only to discover that F15 supplies lots of circuits including A/C, Climate control, Headlamp levelling, Rear suspension levelling, dash etc, etc. So with no diagnostic equipment in the car I had a 14 hour drive back through France and the UK yesterday without speedo so I won't be surprised if I receive a few love letters from the rozzers after XMAS. Thankfully I avoided running out of fuel (due to no fuel gauge).
On thinking about it this morning I realised that blowing a 20A fuse would require quite a heavy load - a pump, motor or compressor - Unlikely to be the dash or any lighting unless there was a dead short or wiring problem. The LC uses the same pump as the Omega for suspension levelling, and has a tendancy to blow fuses when they get old/tired. So I unplugged the compressor, replaced the fuse and tried again. So far the fuse is Ok.
So if anyone has the same symptoms (loss of all dash instruments) and F15 repeatedly blows, try unplugging the compressor. It's under the front bumper drivers side infront of the OSF wheel sh1t shield.