brake lights not working

[chuckle-bus-tom]

Hi all,

I tried searching, tried Haynes and Bentley reading but I can't find a reason why my brake lights don't work. It's a 1991 LHD syncro doka with a 2.1 Mv engine.

I've cleaned all the earths, checked all the fuses and cleaned the connections on the 2 sensors on the master cylinder. Still nothing! Could the switch on the cylinder be dead? The rest of the rear lights work , but I could check the loom I suppose.

[tonytech]

Yes the switch could be faulty, do you have a multimeter? set it to ohms and test it.
Late vans had two switches in parallel (but its not unknown for both to fail)

I assume you have checked the bulbs?

T

[chuckle-bus-tom]

Bulbs are fine yes. I have a multimeter but it's one of those tools I don't know how to use. Can You run me through it?

[clift_d]

Set it to measure DC Volts. With the brake pedal pressed you should see 12V between each of the switch contacts and earth, on both sides of the switch.

[chuckle-bus-tom]

Set it to measure DC Volts. With the brake pedal pressed you should see 12V between each of the switch contacts and earth, on both sides of the switch.

OK, that makes perfect sense so I'll have a look. I managed to make sense of the wiring diagram too, and it runs through a junction in the engine bay so I'll check that's good also.

[chuckle-bus-tom]

I think I'm doing this right. I've set the meter to 20 on the side with a V with a straight line under it. I've earthed the black wire on a spare earth crown point and put the red wire on the terminals of the switch closest to the front of the van, with their wires connected still and depressed the brake pedal. The reading is 11.(various) whether the pedal is dressed or not.

[clift_d]

The wiring diagrams for your van are here:

http://syncrosport.com/info/wiring/VW_T ... _SS_MV.pdf

Page 12 deals with the brake light system. I'm not sure why you're getting 11+V all the time unless one of the switches is stuck permanently closed, but then you should be getting your brake lights staying on. Maybe if you disconnect the wires from one of the switches and try testing again. Also, it might be worth tracking down the loom into the engine bay and finding if you're getting voltage at the connectors back there.

[chuckle-bus-tom]

I'm flummoxed. I did the volt reading at the cylinder switch again. With connectors on I get 12.25 Volts regardless of where the pedal is. Without the connectors I get nothing. But then again I don't know what I'm doing and the job needs 3 hands and eyes that see round bends. It got dark, but having a look in the engine bay the earth cluster looked messy so I cleaned that lot up. I looked in the black box but couldn't distinguish the connector.

As said. I'm flummoxed. I can only think it's the cylinder switch.

[lloydy]

Bridge the spades to the switches with a bit of wire? If the brake lights come on then you know it's the switches.
(This is presuming the switches make contact and not break contact when brake pedal pressed)

[chuckle-bus-tom]

Bridge the spades to the switches with a bit of wire? If the brake lights come on then you know it's the switches.
(This is presuming the switches make contact and not break contact when brake pedal pressed)

I'll try that in the morning. All is pointing at the switch being fubared. I just hope changing the switch doesn't involve changing the brake fluid cos I do not fancy trying to bleed the system!

[clift_d]

Bridge the spades to the switches with a bit of wire? If the brake lights come on then you know it's the switches.
(This is presuming the switches make contact and not break contact when brake pedal pressed)

The wiring diagram suggests they make contact when the pedal is pressed.

[bobswais]

i have had quite a few electrical probs with brake lights etc, but a lot of them were fixed when cleaning up, replacing where needed the earth connector on the side of the body under dash behind fuse box. many terminations there...

[chuckle-bus-tom]

i have had quite a few electrical probs with brake lights etc, but a lot of them were fixed when cleaning up, replacing where needed the earth connector on the side of the body under dash behind fuse box. many terminations there...

I've given them a good going over. I guess it wouldn't hurt to replace a few tomorrow when I'm not rushing, and make sure the screws and connections to the metal are good. I've found in the past that although the connector is good the last few mm of wire is useless.

[clift_d]

I don't think the brake circuit goes to earth until it gets to the rear light clusters and there are no relays in the run that would suffer from a bad earth connection.

[chuckle-bus-tom]

I see on the wiring diagram that it's in the same circuit as the horn, so I traced and cleaned that earth (I happened to also have a non working horn) and everything is good there now. As I said, I gave the engine bay earths a clean, but suspect a couple may benefit from new connections. Being a Swedish import the lights are hard wired in, and although my tail lights are working I suspect the spliced in loom from the ignition to the lights may have fails that are causing confusion.