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Fri Aug 26, 2005 6:53 pm

Ok, so...

I got the wiring harness for my year (1968) from KGP&R. The complete harness, not just the main one. The sub-harness for the brake light switches is meant for a master-cylinder with 3 2-prong switches, as original to the car. I've since replaced the master with one that has 2 3-prong switches, and I can't figure out which wires go where. I've seen the diagram that KGP&$ has on their website about this, but what's throwing me off is that there are 2 blue wires on my harness in addition to the red/black, black, and red ones, and some of them are 2 wires into one connector. Can anybody help me with this?

Sun Aug 28, 2005 11:15 am

The main thing to remember about the dual circuit master cylinder switches is that they operate in parallel to each other. Therefore you can have a hydraulic failure in one of the MC's circuits (either front brakes or rear brakes) and still have braking functionality yet one of the switches monitoring the failed hydraulic circuit will "report" the problem back to your dash light.
SO, both switches are wired exactly the same and this is why you have some shorter "pigtail" wires that are connected to one common female spade because the short pigtail section jumps one switch's connector to the other switch's connector to make them both the same.
The wires should be:
- 1mm black wire comes from fuse #9 (second from right, lower side connection)
- 1mm black/red-stripe wire goes to rear brake light elements (via a connector block usually)
These two are all you need to make your brake lights function. The other wires are used to connect the dash light for testing/failure-report purposes.

Let's consider each 3-prong switch as having a left, a right and a center connection and let's also consider that there is a "front" and "rear" switch as viewed from the driver-side wheel well, while looking at the MC with the switches in place.
Thus, the "front" switch is for the front (disc) brakes and the "rear" switch is for the rear (drum) brakes.
The rear switch's left connection is wired from the fuse #9 via the 1mm black wire and this 1mm black wire should have a short pigtail (maybe the "blue" wire?) to jumper that same left connection to the front switch's left connection. At this point, power is now available to both switches.
Then the rear switch's "right" connection must be connected to the 1mm black/red-stripe wire to the rear brake lights. This wire should ALSO have a short pigtail jumper wire which makes the same parallel connection to the front switch's "right" connection.
At this point, you have power supplied to the switches (both) and a circuit supplied to the switches (both) for the rear brake light bulbs to operate. So when you (ignition on) press your foot on the brake pedal and increase the hydraulic pressure inside the MC it will cause both switches to close and pass electrical current from one side of the switch out to the black/red-stripe wire to make the light bulbs in tail lights work.
In this setup, either side of the MC can fail (no hydraulic pressure) and your brake lights will still work because the "other" side of the MC will still cause the "other" switch to close and pass electrical current to the rear tail lights so the guy behind you will know you are trying to stop.
Now all that is left is the "idiot" light on the dash and this idiot light uses the center connection of each switch and is connected in parallel just as the other two wires were connected.
The dash light gets it's power from the center connection of the rear switch. This would be a 0.5mm red wire normally. This skinny red wire (may be the blue one in your new wire loom) is also jumpered from the rear switch, middle connection to the front switch's middle connection (this parallels the two switches completely now).
At this point, you have wired those two MC switches completely.
Now all you need to do is complete the dash light wiring:
The dash light assembly has three tiny connectors on it:
The bulb's "input" connector is actually grounded to body ground via a 0.5mm brown wire that goes to the emergency light switch at terminal #31.
There is another connector on the brake warning light which is connected via a 0.5mm red wire to your MC's center connectors (jumpered from one switch to the other).
Finally there is a 0.5mm black wire that connects your brake warning light to the emergency flasher switch at terminal #15.
In this configuration (your wire colors may vary based upon who produced the new wire loom). Your dash warning light has two power connections:
- red wire from MC's, center connectors of each switch
- black wire from emergency switch, terminal #15
- brown ground wire from terminal #31 of emergency flasher switch.
Truly, the brown ground wire could be supplied from any consistent ground point on the body metal or even directly to the battery's negative terminal.
The reason for the two power supplied wires is to allow the dash light to light-up when pressed by your finger (black wire) or to light-up if a hydraulic brake failure occurs (red wire from MC).

You'll have to review this and compare it to your new wire loom to see if any of these wires have a different color. Aftermarket wire harnesses usually try to stick to the original wire colors for obvious reasons, but some are different so try to follow it based upon the Black 1mm wire as supply from fuse panel. Black/red-stripe 1mm wire as supply lead to the rear brake lights and whatever is left over as used for the dash warning light. All of these wires will have those short little pigtail jumper wires from one connector to another that may only be 2-3" long.

HTH

Sun Aug 28, 2005 5:52 pm

Thanks much, your breakdown of the break lights worked beautifully. Turns out I hadn't accounted for the differences created by putting a 71-and after (that was the first year of the 2-port master cylinder, right?) master cylinder in a 3-port original (1968) car. I had the black from the switches going to fuse 10 as per the 67-69 wiring diagram in the Blue Bible. Oops.

Mon Oct 20, 2008 5:23 pm

I have 70 vert, and I'm trying to figure out how the wires get up to the fusebox from the master cylinder. Please help! Thanks, Bruce.

Mon Nov 16, 2009 9:47 am

[email protected] wrote:
The wires should be:
- 1mm black wire comes from fuse #9 (second from right, lower side connection)
- 1mm black/red-stripe wire goes to rear brake light elements (via a connector block usually)

This is causing me a little confusion. When I press my brake pedal, fuse #9 blows. I check the wiring diagram and the black wire from the brake light switches should go to #11, not #9. You say here that they go to #9. Do I have the wrong wiring diagram?

Sun Apr 23, 2017 8:54 am

Thanks so much for all this info as I'm trying to figure out my brake warning light. My E switch only has to connector- 1968 ghia conv.
Any sugggestions where else to connect all 3 brake warning light connectors?
AlsoThanks again

Sun Apr 23, 2017 12:55 pm

You already have a thread gong regarding this problem:
https://www.thesamba.com/vw/forum/viewtopic.php?t=677144