Gauges playing up

[badgerboy]

Hi,

Got a really strange fault with my mk1 the gauges; rev counter, oil pressure, fuel and boost don't work until I rev the engine hard say about 4-5k.
Then they work and stay on at idle until ignition is switched off.

I have checked the wiring, which is fine on the gauges as well as engine bay but can't see whats going on. The ecu displays no fault, could it be the ecu on it's way out.

Anyway any help is appreciated, as always !

Cheers
Si