Brake lights not working

The brake switch itself seems to be the most common failure point.  It’s a hydraulic pressure switch screwed into the side of the master cylinder, which is behind the front axle and forward of the pedals.  Most (I believe) master cylinders are set up for two switches, one of which is essentially a hot backup.  In that case you can often solve the problem by simply moving the wires to the backup switch.  If that doesn’t fix it, replacement if cheap and easy, but can allow air into the system.  Inspect the wires to verify that nothing is broken, and check out the switch(es).

Lane's advice is sound, but you may want to check your fuse panel first, as that's an easy fix if a fuse is blown.  Even if your fuses aren't marked, you can check both ends of each fuse holder for continuity with a volt/ohm meter.  By checking the fuse holder, not the fuse itself, you are checking for corrosion.  

If you find a fuse holder that fails continuity, yet the fuse seems intact, remove the fuse, clean the ends, and clean/sand the fuse holder itself by mechanical or chemical means (sandpaper, electrical contract spray, etc.), replace and try again.  If continuity still fails, try another fuse.

A bad ground seems less likely, unless you have a separate ground for each circuit or you have additional circuits open, and you aren't aware of it.  It's more likely a fault on the positive side of the circuit. 

The often used Chinese $5 stop light switches on the master cylinder are junk.  As Lane said there are 2 there (if later dual circuit brake chassis).  Look to see if wires are actually hooked up.  You can test with a voltmeter and have someone depress pedal.  When replacing - do not - use teflon tape - the switch has to be grounded and teflon tape insulates it.

And where, exactly, is the stop light switch?

In about the most inaccessible place on the car.  

Losen (but don't yet remove) the left front wheel nuts.

Jack of the front of the car to get the wheels off the ground.

Remove the left front wheel.

When you look behind the wheel, there is a small shelf and just above the shelf is the brake master cylinder.  On the side closest to you are the one or two brake light switches.  Lord knows how they're wired up on any CMC, but most likely only one will have wires going to it.  As mentioned, you could try switching the wires to the other one - that might work, but as Jim mentioned, try messing with the fuses, first.  It's a lot easier crawling around under the dash than pulling the front wheel.

They originally had nice rubber boots to protect them from the environment

You guys rock!  Thank you for the helpful information on where to look for the trouble spots. I have used a test light to verify that all of the fuses are supplying power. I will try and get to the master cylinder for the brake and check there when the pedal is pressed.  Seems like a common failure point. It may be with all the driving she is getting recently she is shaking things loose.   I will investigate and report. 

R3D

WOLFGANG posted:

The often used Chinese $5 stop light switches on the master cylinder are junk.  As Lane said there are 2 there (if later dual circuit brake chassis).  Look to see if wires are actually hooked up.  You can test with a voltmeter and have someone depress pedal.  When replacing - do not - use teflon tape - the switch has to be grounded and teflon tape insulates it.

The switch DOES NOT need to be grounded. It is a 2 wire switch, it makes or breaks a circuit ACROSS the two contacts. Usually, but not always, one wire is always "hot"(with 12v to it all the time). The other wire goes to the brake lights.

The teflon tape comment IS correct for the oil pressure one-wire idiot light switch. This switch needs to pass a ground through the switch to the engine to make the light turn on under low/no oil pressure.

Easiest way to check it is with a test light. Pull the wheel as Gordon says, and either probe the 2 contacts, one at a time with a test light(or a multimeter on DC volts) with the wire of the test light to ground(or other wire of multimeter to ground). 

If the light lights or meter reads 12v, you are good and have power. Next, put your probe or multimeter to the OTHER contact on the switch. Then have someone step on the pedal. Test light lights or meter reads 12v, then the switch is good.

If the taillights don't light and the switch tested good your problem is wiring/ground/bulbs/bad taillight sockets.

Here's wiring diagram.  There are 2 and 3 prong switches.  The 3 is used for the VW dash brake faiilure warning light.  If wired like this - one switch could be bad and brake lights could still work.