The black/yellow should provide 12V for most of the things you've got that don't work.

There should be an inertia switch in the spare wheel well. If there isn't one there, have a look in the area of the driver's side kick panel - later injection looms have one there (shouldn't be there for your car unless a later loom has been fitted, or the car loom wasn't originally for a car with fuel injection). If you can't find one, then check the voltage to the fuel pump at the yellow relay on the passenger side behind the glove box, and at the connector for the engine loom to car loom (should be a black/red wire).