I’ve had it since I bought the car a couple of years ago. It is activated through an oil pressure sensitive brake contact placed on the front torpedo plate in the engine bay. Supposedly these are very reliable and should not easily wear out. But I had to push the pedal very hard to make them shine, so I’ve replaced the contact twice. Still same problem. Here’s the contact and a typical brake system.
My braking system was restored around 2005 with new pipes etc so there’s no leakage etc. Works perfect which became evident in a panic brake incident caused by a young smiling woman governing a huge Volvo XC90 accelerating into the street from nowhere. Screaming tires but the 50+ year old car stopped just before the crash. The brakes work perfectly but not the lights.
Anyway, this autumn service I had a tip from Mats Eriksson from the Swedish P1800 club to air the brake system at the contact. Usually you do this at each brake to make sure no air is caught in the system when you have un-even brakes. Now 3 months after the service the brake lights is still immediate. So there’s a tip before replacing the contact.