Brake Warning Light

I took my car to the garage for some minor work which didn't involve anything to do with the brakes but now the brake warning light is on all the time. I have done a search on the forum and found reference to the Brake Warning Valve for the P1800ES. The brakes seem to work fine, there is no apparent leaks and no fluid loss so I thought rather than waste trips to and from the garage I would have a go myself. In the other thread it suggests removing the warning switch from the valve, pump the brake pedal a few times and reinsert the switch. This will allow the shuttle inside the valve to return to its correct position so when one screws the switch back in the circuit remains broken and the light will be out. Seems quite straight forward ( famous last words !!! ). My query is that I am assuming that the brake warning valve on the P1800 is the same as that used on the 240, does anyone know if my assumption is correct ?

Resetting 

Hi, haven't had anything to do with non 200 valves but the proccess is the same. Valve is at base of LHF subframe near firewall and the switch unit is accessed via the hood (but a long way down). Contacts are spring loaded so beware when removing the switch unit. Sometimes the piston tends to stick off centre so the unit does not reset. Can be awkward if that happens.

There was a thread a long time ago, either here or at brickboard.com, on the cussedness of these valves. The consensus was that they tended to stick over in one position once activated, through obvious lack of use. There was a warning about unscrewing the switch, that it was difficult to stop it leaking, and very difficult to re-engage the threads. I recall that as an experiment I tried unscrewing my spare unit, and confirmed that this was indeed so. The switch is made of hard plastic, which is difficult to start in the threads, and very tight. It was suggested that having ascertained that there really was no fault in the brakes, the easiest solution was to disconnect the wire or take the bulb out. The initial triggering is caused by an imbalance in the pressures in the two brake circuits, in this case presumably only a momentary difference, not indicating an actual brake fault. I did suggest that a way of re-centring the sliding piston would be to lever back a brake caliper piston on the appropriate circuit, and then stamp on the pedal. This would pressurise one circuit immediately, but not the other because the caliper piston would have to take up the clearance first. The shock, if applied on the correct side, MIGHT re-set the switch. Just an idea - I don't know whether anyone has actually tried it.