Brake lamp on instrument panel, 71 bus

I've been tidying up the instrument panel on the Wonderbus. The 71 model year, unlike the previous model year has a brake lamp on the instrument panel (in the US, anyway). I don't have a 71 Owner's Manual, only the

1970 manual. I presume that this lamp is meant to warn of low brake fluid or pressure or something.

This is a three-wire device. The wiring diagram does not clearly show all three terminals. It shows a Brown wire, which is chassis, which connects to the terminal on the bulb holder itself. There are two other terminals on the body of the device, labeled "15" and "K" (had to put on my Dr. Frankenstein magnifying goggles to read them).

I presume that the black wire (switched 12V) is meant to be connected to Terminal 15. And the red wire, which goes to items "F" on the wiring diagram ("Brake light switch with warning switch") would go to Terminal K.

This wiring, and the construction of the lampholder, indicates that you should be able to test the bulb by pushing in the lamp lens. Right now I'm not getting any lighting of the bulb, yet it is a good bulb.

I guess I'm asking for someone to confirm that my understanding of the wiring and operation is correct. Then I can poke, probe, and threaten until this potentially useful warning lamp becomes functional.

Reply to
Mike Rocket J. Squirrel Elliot
Loading thread data ...

Have you checked this one?=20

formatting link

Reply to
Olli Lammi

Rocky, Don't forget to turn ignition switch to "on position" to do your trouble shooting. :)

"Wild" Bill and "Blondie" Linda Tucker

President and First Lady Rare Air VW Club Pensacola, FLorida

'78 VW Bus ( "Old Rusty" )

'76 Bug Resto Custom ,1776, Front Disc, T-3 Rear brakes, "Prowler Purple."

'69 Squareback , Arizona car, Automatic, "Blondies' Car"

'67 Squareback

Rare Air VW Club Website:

formatting link
or

formatting link

Reply to
Wild Bill

Correct on all counts. Don't overlook the possibility that the push-to-test switch is bad.

Look on my web site for: " Wiring of 3-prong brake light switches ('70 and later) with warning light connection. " It shows how the brake switches operate the warning light (push-to-test not shown.)

Speedy Jim

formatting link

Reply to
Speedy Jim

Thanks, Olli, that's the wiring diagram I use. The brake lamp symbol does not clearly show the three terminals.

Reply to
Mike Rocket J. Squirrel Elliot

Ok. Then this 73-onwards diagram has the lamp-test-switch with 4 wires. The terminal numbers and wire colors are there.=20

formatting link
Better check Speedy Jim's site though. ;)

Reply to
Olli Lammi

Thanks, Jim. Digging into this a bit more deeply:

Bentley's writes that, ". . . each axle has its own hydraulic circuit," and "The system is so designed that leaks on one circuit cannot affect the other. An electrical warning system in the master cylinder causes a red warning indicator in the instrument panel to light up if hydraulic pressure is too low in either brake circuit."

With neither switch activated, as shown on your wiring diagram, +12 is connected to Terminals 81a and goes nowhere.

When the brakes are applied, and if both hydraulic circuits are working, then both switches activate, connecting Terminals 81 to 81a, which applies +12 to the rear brake lights.

If one brake switch fails to activate (front or rear hydraulic circuit) then the rear brake lights and the warning light all light.

But if both hydraulic circuits fail neither switch is activated and neither the rear brakes lights nor the warning light receives power.

I guess that in such a situation a warning light would not be very useful; the driver would know that the brakes are no longer working because the vehicle would not be slowing.

Reply to
Mike Rocket J. Squirrel Elliot

Hmm . . . exciting new wire: 61!

Reply to
Mike Rocket J. Squirrel Elliot

You got it all right again!!

Speedy Jim

formatting link

Reply to
Speedy Jim

Wire #61 is a red herring on your year Bus. Does not apply...

Speedy Jim

formatting link

Reply to
Speedy Jim

Found the problem: the black wire which is meant to provide +12 to the warning lamp for the push to test function was broken off at the switch end -- down on the master cylinder. E-Z 2 fix, but I also noted that the rubber boots meant to cover connections on the plugs that connect to the two brake switches are all kinda rotten. Need to replace. Aircooled.net has brake light switch boots, but they are as "Used on Type 1s, 3s, and

4s." Anyone know where I can find Type 2 brake light switch boots?
Reply to
Mike Rocket J. Squirrel Elliot

Mike Rocket J. Squirrel Elliott wrote: but I also noted that the

Type 2 uses the same switch; I gotta think the booties are the same...

Jim

Reply to
Speedy Jim

Thanks.

Reply to
Mike Rocket J. Squirrel Elliot

Exactly right!

-

----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

-----------------------------------------------

Reply to
Jim Adney

MotorsForum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.