How do I check the brake warning switch? I have removed it and bled brakes after doing front hoses and pads but the brake failure lights are still on. Should this have rest it?
Generally, you have to physically remove the switch and put it back in again.

You do that once you're sure that pressure is gonna be equal on both sides - like, the red and the blue in this pic.




And then hope that either of the pistons in the brake line junction haven't sheared the pin off of the brake failure switch.
Your last comment interests me. When I had it out for bleeding I had a feeling it looked broken off. If this was the case wouldn't the light be off though?
Nope. The pin has to be pushed in for the switch to stay open circuit.

When the pin is broken off or it's all the way out, the circuit closes and the light comes on.
OK. makes sense then. As the valve seemed to be centralised. Thanks for that.