Well, I've got a little further. It doesn't plug in to the back of the steering wheel and it doesn't plug into the back of the speedo. Where on earth does this thing go ?!

Thanks Frank & Charlotte. Yes, I trust the cassette is ok - my first task is to plug the connector back where it belongs. I'd rather not take off the whole dash to find out where that is. Does anyone have a good picture of the back of the instrument binnacle? The workshop manual only has a...

OK, I think I've found the problem. A 9 pin female multiplug with 6 active pins is dangling disconnected. It's under the steering wheel and I can't see what it plugs into. Looking at the main circuit diagrams for 1990 model year RR, it seems certain that it's for the cruise control...

Yes, I found the switch on the brake pedal (it's the lower of the two, with a single vacuum line coming off it). Tested it with a multimeter and it delivers 12V when the panel switch is on and the plunger is depressed to close the circuit. So the current's getting to the switch correctly. Now...

I suspect not, but the easiest way to check is to take a working bulb from an adjacent switch so you can eliminate it as a possibility. I'm trying to fix my cruise also. Have checked the vacuum bulb and the vacuum lines and no cracks apparent anywhere; the vacuum on the bulb is holding fine...