That right there is very likely the problem in itself
They take so little current to light that your switch can have just enough of a current path even when it ought to be open.

just for fun put a (real not LED) test light from ground to the brake light wire and see if that is enough load to keep the brake lights off.
If so you can still try replacing the switch but it may happen again.


1951 GMC 250 in the Project Journals
1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-