Brake Warning Light issue

[Tim Donahoe]

The last two times I started my 1974 Super Beetle, the brake warning light stayed on for a few seconds (the first time). The second time, the light stayed on for a good thirty seconds.

The brakes work as well as they always have since I installed a new ATE mc, as well as a front disc brake conversion, new rear brakes, flex lines—but, I reused the old brake light switches at the mc. This was all done about five years ago.

The brake warning, alternator, and oil lights have always come on when first starting the engine, of course, but now the brake light wants to stay on awhile longer. Thirty or forty seconds. Then it goes out like always.

Anyone else had this happen?

Tim
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Richard O'Brien

[vwoldbug]

Try unhooking the stop light switches one at a time when you start it .

[Cusser]

I've always found/considered that dash "brake warning light" to be semi- to non-functional. Driver should know by brake pedal feel if something's amiss.
_________________
1970 VW (owned since 1972) and 1971 VW Convertible (owned since 1976), second owner of each. The '71 now has the 1835 engine, swapped from the '70. Second owner of each. 1988 Mazda B2200 truck, 1998 Frontier, 2014 Yukon, 2004 Frontier King Cab. All manual transmission except for the Yukon. http://www.thesamba.com/vw/forum/album_page.php?pic_id=335294 http://www.thesamba.com/vw/forum/album_page.php?pic_id=335297

[kreemoweet]

Try disconnecting the red wire from the brake light switches at the warning light, and see how it works. If the
problem continues, then at least you'll know it's not a malfunction in any of the braking system components.
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'67 bug: seized by the authorities
'68 bug: seized by the authorities
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[vwoldbug]

Tim , can you try revving the engine when starting and see if that changes anything .

[Evil Clown]

You know you can make the warning light
come on by pressing it with the key on

Don't know if there's a reset by doing this
but it may be stuck
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CARRY ON

[ashman40]

FYI.. in some cars the Brake Warning lamps are also wired into the "parking brake switch" which is grounded when the brake handle is UP. Check the pressure switch below the parking brake handle (looks like a door jamb switch). Look at the raised Phillips head screw in this pic:

If the switch is allowing the wire from the Brake Warning switch to ground while the handle is DOWN it could be the cause of the light remaining ON. Or, maybe you were not aware the parking brake was linked to your Brake Warning Lamp and it remains ON until you drop the parking brake handle. So this extra time is actually the time you are warming up the engine with the parking brake still set? Maybe the switch is working as designed?



Here's a diagram of the later (improved) Brake Warning light circuitry from Speedy Jim's site:

12v ignition switched power comes in on the #15 terminal at the top (so this circuit is only operational while the ignition switch is ON). When positive current is allowed to flow thru the bulb to ground either out the left path (#61) or thru the transistor to #31 at the bottom, the lamp will turn ON. Pressing the bulb shorts the output to ground to test the lamp.

#61 is grounded by either the GEN lamp circuit or the OIL lamp circuit (it changed over the years)... or the parking brake switch. The first two circuits are grounded when the engine is NOT running. Once the engine is running the path to ground is OPEN (OIL pressure switch) or there is 12v+ coming back on this circuit (VR) and so there is no path to ground on this path. See FYI above about how the parking brake also can ground this circuit. The diode in the circuit prevents 12v+ from coming IN on this circuit.

The "K" input is 12v+ coming from the brake switches. When there is 12v+ coming in on K it indicates a failure in the brake system (switch failure or pressure failure in one side of the MC). The positive current flows into the right of the transistor and out the bottom to ground (#31). When current flows from K to 31 the transistor will also allow current to flow from the warning lamp to 31. This allows positive current from #15 to flow thru the lamp and turns the lamp ON. If the transistor is failing it could allow current to flow to ground and the lamp would turn ON.

Having described all of this... I think you should look to the parking brake switch first.
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AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[sjbartnik]

[Tim Donahoe]

Ash,my car came with the switch at the parking brake, but it had been disconnected by a PO before I bought the car in 2012. In all this time, I’ve never had the brake light stay on.

However, after reading an old thread, it seems the brake warning light and oil pressure warning light are connected. On the second occasion of the brake warning light staying on, the oil light stayed on a little, too. But it went out before the brake warning light did.

So, I checked the wire going to the oil sender switch on the engine. It seemed fine, but tomorrow, I’m going to check it with a stronger light and see if perhaps it has a bare spot in the insulation.

By the way, I never warm up my engine. I start and go immediately.

Tim
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Let's do the Time Warp again!

Richard O'Brien

[ashman40]

See if you can't disconnect one wire at a time from the Brake Warning light assembly.

Start with the #31 wire. The Brake Warning light should still turn ON while the OIL light is ON, but once the OIL light goes out the Brake Warning light should too. The Brake Warning function will be disabled while #31 is disconnected.

Reconnect the #31 but disconnect the #61 wire. This should disable the link to the OIL light. See if the Brake Warning light still remains ON for a while. If it does it is likely due to the transistor grounding the lamp.

Next disconnect the K wire. This disables the connection to the brake switches. Does this prevent the lamp from turning ON. If there is no change the problem is probably with the transistor. If the problem went away, test the K wire. If you detect any voltage on the K wire it is coming from the brake switches.
_________________
AshMan40
---------------------------
'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[Tim Donahoe]

Ash, I’ll mess with it tomorrow, but from what I remember, my brake warning/seat belt warning light has a push on harness. No separate wires. Perhaps it’s possible to remove the wires separately from the back of the harness, although I can’t tell until I remove the front dash plate and have a look see.

I can remove the oil sender wire at the engine, for certain, though. This should tell me if the oil pressure sender is causing the issue.

Also, I think I have another brake warning/seal belt unit. I’ll break it out if necessary and see—assuming this transistor you spoke of is inside of the unit.

I don’t know if I mentioned it, but I don’t press on my brake pedal when starting the car, so it’s not as if I had the brakes on. I do keep the handbrake on until I’m ready to take off though.

Another possibility is that the connection that connected the missing handbrake switch is still hanging around in the tunnel—and magically started grounding. But that seems unlikely.

Tim
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Richard O'Brien

[runamoc]

According to the schematic, the brake idiot light has two bulbs. One that's powered by #15 and has a switched ground on wire/terminal L from the 'safety belt warning system relay'. The other bulb is powered by #15 also but gets it's switched ground from the 'failed brake' circuit. ALSO one of the switched ground inputs to the 'failed brake' circuit comes from the 'parking brake control light switch' AND has a switched ground input from the oil pressure switch.
My 'failed brake idiot light'

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Yard Art: 2 Sandrails
Outback: '69 Ghia - '68,'69,'70,'72 Beetle - '84 Scirocco, GTI - Pair of '02 Golfs-
VW Wiring = It's just wires

[Tim Donahoe]

Ash, where exactly is this “transistor” located? Is it inside the rectangular brake warning light housing?

Tim
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Let's do the Time Warp again!

Richard O'Brien

[heimlich]

[ashman40]

[Tim Donahoe]

So, the brake warning light has taken a new turn. Previously, it just stayed on when I first started the car, and went out when I stepped on the brake pedal. I moved the oil-sender wire (in case it was somehow grounding). This oil sender wire is connected to the brake light switch, according to Ashman.

Cool. The brake light switch stopped acting up upon startup. Okay, there were no bare spots on the oil sender wire, but after making sure it wasn’t against any tin, the problem seemed to have been resolved. I let the matter go.

Yesterday, however—after a few weeks of no issues— the brake warning light came on and stayed on again. When I pressed the brake pedal, it went out. Same thing as before. But today, each time I let off the brake pedal and pressed down on it, the light would come on again. This was the opposite of my original problem. This time, the light subsequently came on each time I pressed the brake pedal. After three or four times of pressing on the pedal, the light got progressively dimmer until it wouldn’t light anymore.

My brakes are fine. The reservoir is even with the seam, so I have no leaks. Also, I checked each wheel for leaks, just for the hell of it. No leaks. 1/4 inch freeplay at the pedal.

I assumed because of Ashman’s teachings, that since the first time the light came on without pressing the brake pedal, the problem may have been in the light unit (the transistor), but the problem went away. And now, the light stays on after initial start, goes out after pressing on the brake pedal—but comes back on again each time I press on the pedal again. After four or five times of pressing on the pedal and the light coming on at each press, the light eventually goes out and does not come back on the rest of my driving experience throughout the day.

Very strange.

Could a brake light switch that’s going out cause this issue? When I installed my new ATE master a few years ago, I reused my old brake light switches. Could one be giving up and cause these weird symptoms?

And one other thing: If I get out to check after driving, one of my rear drums feels hotter than the other. Not ungodly hot—as if the shoes were stuck on the hotter side—but noticeably hotter on the tip of my finger. I can keep my finger on the cooler drum. On the hotter drum, I have to remove my finger because it’s too hot to keep it on there.

This last was probably not worth mentioning, but I thought I’d throw it out there.

I’m leaning toward a problem with my brake light switch(es). But I hate to waste fifty dollars on two ATE or FTE German switches if that isn’t really the issue.

Tim
_________________
Let's do the Time Warp again!

Richard O'Brien

[vernonc]

Tim, I can't help on the light issue but I just went thru the 'hot drum' problem.
Turns out the pistons in the wheel cylinder had corroded to the point that the springs would not push them back in when the pressure was released. They were ATE cylinders that were less then five years old.

I replaced them with new ATE's but this time I applied a bit of Never Seize to the pistons; hoping this will prolong the cylinder life.

Like everyone says......."things aren't like they use to be". Time will tell.

Hope this helps.

mort
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"Those who don't read newspapers are un-informed. Those who do read newspapers are mis-informed." Will Rogers

'69 sedan, low mileage, all original.....currently being 'freshened-up' for road trips and daily driving...just not every day

Freshening-up link http://www.thesamba.com/vw/forum/viewtopic.php?t=617386

[Zundfolge1432]

[ashman40]

From that current description I'm thinking your brake switches are going bad.

First, find the red wire coming from the brake switches to the brake warning lamp in the dash. There should be a junction just after the red wire leaves the harness coming from the switches. Disconnect the red wire from this junction. Turn the ignition ON and test this red wire for 12v. It should read zero volts. If there is voltage on this red wire it means one of the brake switches is passing voltage over the red wire or to the black/red wire while at rest. The brake switches or the wiring at the switch are bad.


You can test the switches. Use Speedy Jim's diagram as a guide:

Remove the wires from both brake switches.
Set your MM to read continuity/resistance.
At rest, test that:
- #81 and #81a are shorted (zero resistance)
- #81 and #82a are open (infinite resistance)
- #81a and #82a are open (infinite resistance)

Pressing on the brake pedal, test that:
- #81 and #81a are open (inifinite resistance)
- #81 and #82a are closed (zero resistance)
- #81a and #82a are open (infinite resistance)

Do this test for both switches. The results should be identical.
Also make sure your brake switch plug is wired correctly. As shown in above diagram. Look for loose wire strands that could be shorting wires together.
_________________
AshMan40
---------------------------
'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[Tim Donahoe]

Vern, thanks for the tip. I’ll check the wheel cylinder on that side.

Zund, I hear you, but I like having the warning system. Parts, being what they are today—even the best German—just seem to require all the little systems that do their part. Besides, there’s a reason why this is happening, and I want to get to the bottom of it.

Tim
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Let's do the Time Warp again!

Richard O'Brien