You need to be able to get to the contacts where the wiring loom connects.
If you have a test meter set it to resistance, ohms, connect to terminals and move the brake pedal (ignition off). The meter should alternate between 0 ohms (good connection, i.e. no resistance) and infinity (no connection). If the readings are variable or jump about you have a dodgy switch, assuming that you have good connection to the contacts.
If you don't have a meter get a torch battery, bulb and two bits of single core wire about 100-150mm long. Wire the bulb and battery in series and connect to switch terminals. The bulb will alternate between on and off as you work the brake pedal.
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