dash and wiring problems:

[Matraman]

Thanks Roy. It's the left side of the rev counter which isn't illuminated. I saw the unused holes, they both had tape over them. I replaced the bulb with the instrument panel out and it was working on the bench, but back in the car it wasn't coming on. So I removed it with the instrument panel in situ and of course it pinged off somewhere and is hiding behind there. I was hoping not to remove and replace the delicate instrument panel and vulnerable aluminium facia more times than necessary, so I though I should be able to get a new bulb holder for a couple of quid!

Looks like I'll have to get the instrument panel out again for a better look. I've tried driving along a bumpy road to shake the bulb holder out, but no luck!

My car has a choke warning light and no vacuum sensor.

[Matraman]

After removing the instrument panel and air vent (it needed reconnecting to the air supply pipe anyway) I found the bulb and holder perched on a little ledge at the top back left corner behind the dash.
The reason the bulb wasn't lighting up was a bit of the copper at the end of the tab which connects to the bulb holder had come off. The plastic layer was still there. I got a few thin strands of copper wire and attached them to the bulb holder connection on one side, so that they could connect to the remaining bit of copper on the circuit board when the bulb holder was pushed all the way in. It seems to work fine now.