Yes, '66 and earlier cars have that spring between the master cylinder and the retainer on the push rod. Usually that is enough to trigger the brake light switch. If you go to a later master cylinder, you may have to rig up one to work. The original setup had a rubber boot in the mix too and a piston retainer that held it. Most of the later master cylinders aren't able to accept that retainer and boot, but, some are. It's not a big deal, but, if you really want that sealed up like the early design, you'll have to look around to see if you can find a master cylinder that will accept it. I just transferred my spring and pushrod spring retainer to a later master cylinder and let the spring just press against the master cylinder housing.