Brake lights - Electrical

[richard.w]

I've posted this earlier and was about to go down the road of replacing the brake switch, however -
My brother, knowledgeable but living on the other side of the country, talked me through checking the electrics.
Using my voltometer (or whatever) I get a reading on the live element of the brake switch. Going down to the lights I get no reading at the spade connector.
I disconnected the wire and replaced with a new wire going from the brake switch to the the brake connection, there's a reading on the wire. Put bulb in and it works, briefly, then stops. Same happens on other side of van. Tested where the bulb connects into the light cluster, ther's a reading. Put bulb in, works briefly and stops. There's no reading at the spade with the bulb in situ.
Replaced with original wire only for exactly the same to happen. Readings all down the line until I put bulb in.
Replaced all the bulbs, same again.
Sorry it's so verbose, I've just spent a day getting nowhere.
Any suggestions would be most welcome, words of one syllable please!
Many thanks,
Richard

[VWCamperfan]

Put a wire across the brake light switch, keep it there and check lights again. If they stay on, it's your switch.
99% of the time brake light problems are caused by the switch. It operates on brake line hydraulic fluid pressure and can often play up.

[richard.w]

Thanks very much Mark.
When you say put a wire across the brake light switch what exactly do you mean? Do I literally connect the two switch teminals with a wire, switch on and apply the brakes, or am I running a wire down to the light cluster?
I know I'm useless with electrics, but I'd rather not have to give up. Think idiots guide!
Richard

[VWCamperfan]

Keep the two connectors on the switch with just a bit of the terminals showing and connect a wire across the connectors on the switch.
As another option, you can disconnect both connectors on the switch and connect a wire between the two cables you just disconnected. Same as above, if the brake lights come on, it's the switch.
You don't need to press the brake pedal, this test doesn't need you to do that.
As you said, just connect the switch terminals with a wire. Think of it as a light switch, it just switches on and off, same as if you were pulling two wires apart and putting them back together again.

[richard.w]

Very precisely explained. Will have a go tomorrow and let you know the result.
Many thanks,
Richard

[richard.w]

Finished work, had a sleep (early morning shift, not pleasant) and then had a go with the wire across the connectors and yes, the brake lights stay on.
So, it's my brake switch.
I've read as many threads as I can and I can't quite work out whether I need to remove the reservoir to change the switch, whether I could just drain off the fluid and get at the switch through the dash pod opening or whether I go straight for the switch having placed absorbent material underneath and work like fury.
I quite like the sound of the last option but sod's law tells me I'm looking at the first.
Your advice would be most welcome.
Richard

[VWCamperfan]

Have the new one nearby, undo the old one and quickly whip the new one in. You will only loose a few drops of brake fluid.

[richard.w]

Purchased my brake switch, fitted as instucted, hey presto ....there was light at the touch of a pedal!
Many thanks Mark, I'm feeling I've achieved.
MOT tomorrow, fingers crossed.
Richard

[icosahedron]

Glad that you sorted your problem, but there is more to it and never should have reached this stage.

As a safety feature there are two brake light switches attached to the master cylinder. They work in unison and are wired in such a way that should one of them malfunction, the dashboard brake warning light will come on permanently. The functioning switch will continue to operate the brake lights as normal. You can reset the brake warning light by disconnecting and reconnecting it, but if you really have a faulty switch, it will come on again the next time you step on the brake pedal.

In your case both switches were faulty and it seems that you have a problem with the warning light, blown bulb or a faulty unit assuming it is connected. The light might well operate with your handbrake, but there is an additional electronic circuit utilising a thyristor for the brake switches safety function inside the unit.

[VWCamperfan]

Glad that you sorted your problem, but there is more to it and never should have reached this stage.

As a safety feature there are two brake light switches attached to the master cylinder. They work in unison and are wired in such a way that should one of them malfunction, the dashboard brake warning light will come on permanently. The functioning switch will continue to operate the brake lights as normal. You can reset the brake warning light by disconnecting and reconnecting it, but if you really have a faulty switch, it will come on again the next time you step on the brake pedal.

In your case both switches were faulty and it seems that you have a problem with the warning light, blown bulb or a faulty unit assuming it is connected. The light might well operate with your handbrake, but there is an additional electronic circuit utilising a thyristor for the brake switches safety function inside the unit.

Only on dual circuit braking system with handbrake warning light. Not all of these vehicles have them and most only have one brake light switch.

[richard.w]

Thank you.
Sailed through the MOT, only cost - one switch and the fee, Hurrah!
Thanks again.
Richard

[MarkyBoyT25]

hello im on my third switch, dont think it needed the last one just some fluid

anyway how much did it pi## you off getting it out and screwing the new one in?

i really wanted to pull my hiar out, did you use a special spanner?

i couldnt get a socket on it

we dubbin it!

[richard.w]

Hate to say but it was straightforward. Removed the cradle holding the speedo and light switches (four screws), eased it up and got a bog standard spanner on the switch. It was original, perhaps the quality made it easier to get out. Fyi VW Heritage have originals at £17+ with 48 order time, I couldn't wait and my garage ordered one at £11+. I just hope the quality is there!
Richard