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mickey12 Samba Member
Joined: August 22, 2015 Posts: 80 Location: Kansas City
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Posted: Sat Jun 19, 2021 12:37 pm Post subject: Three prong brake wire help |
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I have a ’68 bug with two-three prong brake light switches. Help, by the numbers, which wire goes where?
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Michael Ambrozik Samba Member
Joined: October 17, 2020 Posts: 631 Location: San Jose, CA
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Matt Wilson Samba Member
Joined: November 14, 2005 Posts: 2408 Location: Colorado
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Posted: Sun Jun 20, 2021 9:12 am Post subject: Re: Three prong brake wire help |
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Do you have a brake warning light on the dash? I found this diagram to be helpful, although you may need to chase the wire connections and proper terminals down, as well as get the rubber boots.
_________________ 1972 Standard Beetle
1969 Baja Beetle |
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mickey12 Samba Member
Joined: August 22, 2015 Posts: 80 Location: Kansas City
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Posted: Sun Jun 20, 2021 10:50 am Post subject: Re: Three prong brake wire help |
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thanks for the research. Got some OEM wire and a new main harness, working through the mess. Let you know what happens. |
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Matt Wilson Samba Member
Joined: November 14, 2005 Posts: 2408 Location: Colorado
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Posted: Mon Jun 21, 2021 10:35 am Post subject: Re: Three prong brake wire help |
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The switch end of the wires uses those tiny female spade connectors, which can be a little fragile. I'd suggest testing the bulb before you get it all back together too. _________________ 1972 Standard Beetle
1969 Baja Beetle |
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Michael Ambrozik Samba Member
Joined: October 17, 2020 Posts: 631 Location: San Jose, CA
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Posted: Mon Jun 21, 2021 1:45 pm Post subject: Re: Three prong brake wire help |
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The right switch will use .25 connectors not .110 |
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sb001 Samba Member
Joined: May 19, 2011 Posts: 10406 Location: NW Arkansas
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Posted: Mon Jun 21, 2021 7:56 pm Post subject: Re: Three prong brake wire help |
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Here is a good diagram showing the way the 3 prong brake switches are wired:
http://www.speedyjim.net/schem/2brake.gif
Solid black wire coming from fuse block splits and goes to 82a terminal on each brake switch, this provides power to each switch
Black wire w/ red stripe comes off each 81 terminal, they join together and go to the rear brake lights. When you press the brake pedal the hydraulic pressure closes the switches and current travels through the brake switch from 82a to 81 and goes to your rear brake lights lighting them up.
Solid red wire comes off each 81a terminal, they join together and go up to your brake warning light on the dash. If one of your brake circuits fail, the current travels through the GOOD switch but then instead of going to your rear brake lights, it goes up to the brake warning light on the dash instead.
Here is another diagram of how the system works (upper left graphic shows the way the current travels when one of the circuits fails):
http://www.speedyjim.net/schem/3brake.gif
P.S. Being a 68 your dash brake warning light should only have 3 terminals, the one pictured above with 5 terminals is for a later model where that light also functions as a parking brake light.
I am unsure what some of those wires in your photo above are- some of them do not match the factory wiring colors. _________________ I'm the humblest guy on this board.
1969 autostick sedan, family owned since new
1600 SP engine
Solex 30 PICT 3 carburetor
Bosch 113905205AE autostick distributor |
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sb001 Samba Member
Joined: May 19, 2011 Posts: 10406 Location: NW Arkansas
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Posted: Mon Jun 21, 2021 8:05 pm Post subject: Re: Three prong brake wire help |
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Starting in 1970, VW realized that they did not have to use three 2-prong switches as they had been doing (two pressure switches and a third switch for the dash warning light.) They could get away with just using two 3-prong switches, and wiring them so that they still activated the dash warning light when one circuit failed (see diagram I linked above.)
So they began manufacturing master cylinders with provisions for only the two 3-prong switches, eliminating the third threaded hole for the third dash warning light switch, and aftermarket manufacturers followed suit.
If the master cylinder has been replaced pretty much anytime in the last few decades, it is probably the newer style two-switch thereby necessitating the use of the two 3-prong switches. _________________ I'm the humblest guy on this board.
1969 autostick sedan, family owned since new
1600 SP engine
Solex 30 PICT 3 carburetor
Bosch 113905205AE autostick distributor |
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