According to the 1966 repair manual schematic (sec 120 page 48) there is no circuit for a parking brake warning light on the 1966 F/S models. However on the 1967 repair manual schematic (sec 120 page 27) it shows the wire to the switch (tan w/black stripe) is a ground feed and also piggybacks the brake failure switch. It seems when the switch is released (pedal down) it completes its circuit to ground through the pedal bracket illuminating the bulb. The positive is in a buss bar in the printed circuit behind the speedometer which is a master for all the indicator lights. All the functions of the indicator lights work from ground. Use an ohm meter from the connector on the wire to the switch body to insure there isn't an open in the circuit. You may have a very late 1966 car with some 1967 features or there isn't a light there at all! Use a flashlight on the gauges and look for a brake light in there somewhere, you might not find one. If not problem solved!
The buss for the indicator lights works off the wiper fuse in the fuse block and is on a pink wire. It will only be powered up with the key in the run position. - Bill