Ur quattro dash erratic

[StoutyBoy]

Hi

Just got my 86 ur quattro back after a lot of recommissioning work. It's not a finished job yet but is now running properly with an mot by a respected firm.

The car has come back with a dash fault that it's never previously had and looks, to me at least, like an earth issue. Have had discussions with the garage and they had seen in themselves.

When the car starts the dash is fine for a couple of minutes and displays all values for revs, fuel, boost etc. Then it goes a bit wonky. The values all go off the scale .. Revs sit at 5k, fuel value doubles and boost and temp are off the top of each scale. Mph also wildly out. The display is fine but just incorrect values.

I've had the car 22 years and the dash has never been a problem. The car hasn't been used for the last 9 but was regularly run up and the dash was always fine. A lot of work has just been done over an 8 week period, mostly underneath and hydraulics etc.

Would welcome any pointers but I suspect iffy connections and/or earths?

Thanks