1968 Beetle Brake light debugging question

[mrdctaylor]

Ok guys. I've done some research online. Found wiring diagrams. Searched this forum. I'm stumped.

I have a pretty much stock 1968 Beetle that has been in the family since it was new. I *CANNOT* get the brake lights to work, although my dad swears they were working just 2-3 days ago when he got them inspected. Here's all the info that I can think of that might help:

- Obviously I checked the bulb first. Also, all other rear lights work, although I am current missing a bulb in the driver's side back-up light. Blinkers, tail lights, back-up lights all work.
- I am not getting power at the bulb socket that I can tell. I am getting power to one of the terminals on the middle bulb (brake/tail) which I assume is what is powering the tail light. The other tab gets no power.
- I tried taking the wires off of the master cylinder and touching them together to see if it was a bad switch. That did NOT light up the brake lights. So it *appears* that the switch is OK. I also tested voltage with/without holding down the brake pedal and the switch seems OK as best I can tell.
- I took the correct wire (according to the diagram) out of the junction box near the rear-driver wheel in the engine compartment and was not getting power there.

If I've debugged correctly, it seems that the issue lies elsewhere. Two things I'm thinking of:
1) I've read that grounding is weird with these tail lamps. But the lights OTHER than brake lights are working. *COULD* it still be a ground issue? But if it were, wouldn't I see power at the junction box?
2) The brake fluid reservoir was empty and we refilled it. It doesn't appear to be leaking, but the car had been sitting a while. That was the *ONLY* thing we'd done since my dad had it inspected a few days ago when the brake lights were working. Could adding fluid somehow have damaged the brake light switch?

HELP!!!!! (and thanks in advance!)

[Marc]

First question: does the car still have the factory master cylinder? The one with three 2-prong switches? Or has it been replaced with the only type that's been available for ~35 years, the late`69-up type with two switches? If it's been replaced, wiring modifications would've been necessary to keep the warning lamp on the dash functional (and the later-style 3-prong switches fitted).

Speedy Jim has some excellent articles explaining the function of the stoplamp & warning light operation with both setups at his website
early: http://www.nls.net/mp/volks/schem/4brake.gif

late: http://www.nls.net/mp/volks/schem/3brake.gif

Regardless of which setup you have, if you apply power directly to the black/red-stripe wire that goes into the main harness (in the trunk, outboard of the steering column) both brakelamps should come on. Until that's happening there's little point in fooling with anything up front.

[mrdctaylor]

So are you suggesting that I run a wire from the battery to that wire and see if the lights light up?

[mrdctaylor]

And so I'm crystal clear, if I ran a wire from the battery to the terminal back by the engine compartment that would be a good test--and safe?

[mrdctaylor]

OK. I just did this. I connected a wire to the positive terminal of the battery and made a connection with the wires in the little connector/junction behind the firewall of the engine compartment (on the left side looking at the engine) and the brake lights lit up fine. So that is working. Ideas?

[mrdctaylor]

Also there are 2 switches that I see on the master cylinder with 2 terminals.

[Dale M.]

You are making this too complicated.... Remove two black wires with red strip on them and use jumper wire to tie the two together (bypass switches) .... lamps should light....

IF not check fuse.. Should be one next to steering column....

IF good check for voltage at "jumper" and T3 or T4 connectors....

http://www.thesamba.com/vw/archives/inf ... g_6869.jpg

Tool like this can be your best friend...



By the way this is not computer software, its not "debugging" that we do here, its "trouble shooting"....

Dale

[mrdctaylor]

Ha! You can tell I'm a programmer, can't you?

Ok. I already removed the two wires from one of the switches on the master cylinder and linked them with a wire. The lights did not light.

I've checked the fuse. All fuses look good. Also, it should be on the same fuse as the blinkers and they work.

I checked the voltage and was getting voltage on the front side of the switch on the master cylinder. I was also getting voltage on the backside when the brake was depressed (at least I'm pretty sure I was--it has been a long day).

I checked voltage at T3 and was getting nothing. However, when I put my 12V wire that I temporarily attached to the batter to the connection at T3 the lights lit up, so everything seems OK from there on back.

I plan on testing my switch again and the voltage around the switch. If it tests out, I'm stumped. It is just such a coincidence that it was working 3 days ago and then I add brake fluid to the empty reservoir and now it is not working. :-/

[Steve C]

Hi

Are you using a test light or multi meter? A test light is better in these instances because if you have a high resistance joint a test light will not work, but in some cases multi meters show battery voltage as they take less juice from the circuit and don't load connections, the very reason that they are used in electronics.

I'm not sue about your model bug but on later ones there is twin connection near the master cylinder reservoir and light harness where the brake light hook into the harness.

Steve

[mrdctaylor]

Using a multi meter. I will get a light and do some more testing.

[Marc]

If your M/C only has two switches, it's been replaced with the later style but they used the original type 2-prong switches and didn't do the wiring conversion to make the dashboard warning lamp functional - you'll probably find a small red wire and a small black wire that are not in use.
This won't have any effect on the operation of the brakelamps (in fact, 1967 bugs had a slightly different dual-circuit M/C which used two 2-prong switches. Dale's right, a testlamp is better for troubleshooting vehicle electrics - you may find the problem is something as basic as a high-resistance contact point at the fuse...

[mrdctaylor]

You are correct. I saw some wires that must have gone to the warning light. It is disconnected.

Do you mind explaining what you mean by "high-resistance contact point at the fuse"? I don't know exactly what you mean--or how I would correct that. Sorry. Just a quick explanation should do if you have a minute to spare. Thanks!

edit: are you talking about corrosion on a connector causing high resistance?

[Marc]

It's a regular maintenance item (or should be, especially in damp climates) to take out all the fuses, shine up the brass contacts on the fusebox, and bend them together slightly so they hold the fuses tighter. Clean the ends of the fuses too, replacing any that show serious wear.

[mrdctaylor]

What do you use to clean the brass contacts on the fuse box? Another question: is it possible for some things on a particular fuse to work but there not be power enough for other things to work (e.g. the brake lights)? That's probably a stupid question, but what the heck.

[mrdctaylor]

Update--I have it working!

Whew. It turns out that the switch is OK, but the connections at the switch were gunked up and corroded a bit. I cleaned those connectors off really good and the brake lights started working. Voila! Thanks for everyone's help!