I suspect you may have an intermittent earth issue..?
The earth is usually carried via a black wire that loops along the instruments before making contact with the bulkhead or similar earthed metalwork....
IDENTIFY one of the black wire loops connections at the rear of the instruments which may be attached via the instrument clamping screw.... Once identified attach a length of wire at that point, and touch the other end of your temporary wire to bare metal in the local area, perhaps a bolt holding the steering column to the bulkhead..?
If the lights illuminate then you know it is an earth fault...?
Do not connect to any other colour of wire...or you may blow a fuse..or worse..!
