Brake light problem

[Handfull 54]

My 54 truck has only 1600 miles on it. The other day I noticed the brake lights work then don't work. The brake light switch is one of those waterproof kind. I got under the truck and when the brake lights did not work I touched the part that is against the brake arm and it worked. Then I come back later and try the brakes and no brake lights. I pump the brakes and they work. Then later they stop working. The taillights are fine no problems. All the wiring is new from Painless and everything else electrical works fine. Any ideas? Thanks.