Hi HZ,
I agree that it sounds like a faulty brake pressure switch that should be replaced or an electric switch added.
A number of years back I was interested in wiring a “roll-over” switch into my fuel pump circuit. When scavenging for the switch in the trunk of a late 70s Ford Crown Vic (the Ford had the switch behind the driver‘s side trunk panel), I found an electric brake switch that seemed to be new. Bringing both home, I wired in the roll-over and then created and fitted a bracket to the air plenum that positioned the switch in line with the edge of the brake peddle. The new switch was wired parallel to the original pressure switch so that original wiring to the pressure switch would be maintained and providing the benefit of having either switch to activate the brake lights.
Although the unit presented by Hans is one used by many, other units can also be scavenged and used at a very reasonable price (in most cases $0). In my experience, I have found the original pressure switch to be very reliable ….to a point of failure. The trouble is that it will fail and you won’t know it. I suggest that, since the new pressure switch replacements seem to have a much shorter life span than the originals, all should install an electric brake switch as soon as possible. Since it is wired in parallel, it can easily be removed for a concourse event.
All the best,
Ray (64BJ8P1)
P.S. I also recommend the installation of a roll-over or interrupter switch on the fuel pump power connection as well.