Brake light relay?

SOURCE: 2001 vw beetle brake lights not working

Actually, the switch you are referring to will cut the brake lights off when depressed, it is when extended that it will make contact, and light up the brakes. However, if it does nothing at all no matter what it's position, check the wires leading to the switch, and check the switch itself. If it lights up the brakes when you pull the switch off the rail, then you just need to readjust it, so that when you push the pedal, the stem is high enough to ride down with the pedal bar.

If the switch won't pass any current, simply replace your switch, and make sure that when you put the new one in, to adjust it's height above the pedal rail.

SOURCE: headlights wont come on and bright lights won't stay on hold bright light switch and blower works

I had the same problem. The solution is simple; the ignition switch needs to be replaced. This is an easy do-it-yourself project. Here are instructions:
http://forums.vwvortex.com/zerothread?id=2532481
Check for a switch on ebay, they are about $15. After 10 years they wear out.

SOURCE: 2003 Diesel Passat - Brake lights out/Glow plug & ESP lights on

you have a bad engine earth

SOURCE: glow plugs warning light + brake lights on

I had EXACTLY the same problem with a friends car i was doing work on.
Your problem is almost certainly a faulty brake light switch. This is a common fault and brings on the dash lights you describe. The switch is located just above the brake pedal and is easy to fit. If you can get the OBD codes read...My guess is it will show up this switch as faulty.
Good luck
John

SOURCE: reverse lights on my vauxhal corsa v reg are not working

On the side of your transmission will be a switch with several wires coming out of it. This is your reverse switch that turns on your reverse lights and most likely needs to be replaced