Intermittent earth problem?

[kit]

I have an intermittent problem with the dash lights as in they work for months and then they don't work for months, they are currently working fine but they sometimes come on with a short delay after the lights go on and for a while only the centre one came on, now it appears (or rather it doesn't) that the headlight tell tale light is not working.
So is there an earth from all the dash lights, I have cleaned the crowns behind the fuse box and the 12 pin plug that connects the PCB ribbon looks good anywhere else I should be looking? Thanks.