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172 Ph2 electrical issue, no dash. possibly UCH?

  Ph2 172
Hi all,

I have a fault with my ph2 172. sorry for the long post- want to include all the details. Car has been off the road for a long time but battery gets charged and engine started regularly.

Yesterday I jumped in, some ignition lights came on, started engine. I noticed the dash seemed dead, all these where inoperative:-
Instrument cluster backlights
mileage display
speedo & rev counter
fuel gauge
temp gauge

I tested some switches, these still worked OK:-
exterior lights/ fogs
roof light
elec windows/mirrors
indicators (but no usual clicking?)
A/C heater panel

Turned off engine for a few mins. re-cycled ignition, then immediately engine now wouldn't start/crank over? There was No immobilizer light at all and now no electrics as before- no lights, wipers, central locking. BUT both Fog lights worked? :unsure:

After scratching my head and searching on here, I have:-
Checked all the fuses at passenger dash fusebox & engine bay fuses/relays. None blown, no corrosion or loose.
Checked under glovebox at UCH plugs & relays, gave them all a wiggle, unplugged & refit. all secure, no signs of water/loose contact.
Tested main battery voltage again, battery ground point & earth straps- all ok.
Tried both keys.

I left the car overnight. Come to it this morning and the car is now back to the same first stage-
Central locking now working with both keys.
Engine now starts and runs, alternator charging ok.
all side/dipped/high beam lights, wipers, windows ok.
Immobilizer light is back flashing as normal with key out. once engine is started, light does not stay on or flash.
hazards & indicators work but no clicking/beeping.

All these are still INOP:-
Instrument cluster backlights, mileage display, speedo, rev counter, fuel/Temp gauge, engine management light at any key position

I have removed the UCH for a closer look. opened it up and not found any signs of moisture/ corrosion or damage.
I was thinking to check the back of instrument cluster? but I get some dash lights with the ignition on- some are possibly missing.

Is there anything else I could check? or is this most likely the UCH?

any help would be appreciated,