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Old 09-22-2014, 10:52 AM   #1
phookajoe OP
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Cry Master Cylinder Cap Electrical Connection

This is my first post to this forum as I have just aquired a custom 75 R90/6. I have been trying to get it into shape to clear Alberta Out of province inspection. My last jimmy rig task is to get the front brake to engage the rear brake light.

The problem is the wiring harness is totally not OEM. I have an under the tank master Cylinder. the cap has one connection. I am wondering how this type of cap is connected to the electrical system? Is this the correct cap for my model? Is there any other way I can connect the front brake so that it will turn on the rear brake light?

Any assistance would be greatly appreciated.

Rick
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Old 09-22-2014, 11:05 AM   #2
Big Bamboo
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The wiring to the cap is for the brake failure light on the original instrument cluster. It indicates low brake fluid level. Your cap is broken, there should be two connectors there. There should also be a switch activated by the brake lever at the perch, or one screwed into the body of the master cylinder.
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Old 09-22-2014, 12:15 PM   #3
chasbmw
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One of the wires to the master cylinder cap is the earth connection to the instrument warning lights. I had lots of fun and games when I removed the undertank MC from my bike until I realised this.
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Old 09-22-2014, 12:29 PM   #4
phookajoe OP
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Looking for some options to get this past inpection

Thank you for your responses. so it would seem the issue is not the Cap as my gauges are very much gone. The person who did the build removed all of the switches from the controls that includes the location for the front brake switch.

What would a good work around be.
I would like to by pass the master cylinder all together. I would like to switch the controls to something like this : http://www.ebay.ca/itm/22mm-7-8-Adju...32d298&vxp=mtr

These have the switch for the front brake. I guess I will have to compensate for the throttle setup as well.

Am I over thinking this or is there a easier interim fix I might look at?

thanks again rick
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Old 09-22-2014, 12:40 PM   #5
motor_chris
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Interesting looking bike, you have got to give us some more photos.
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Old 09-22-2014, 12:53 PM   #6
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Some photos as requested

As you can see it is a long way from stock so I'm open to suggestions. Just got it few days ago and would love to ride it before the snow flys :)
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Old 09-22-2014, 12:54 PM   #7
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Another from my favorite angle.

Another from my favorite angle.
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Old 09-22-2014, 01:33 PM   #8
silverhead
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The original switch for the brake light was inside the master cylinder.

61 31 1 244 334 is the part number

Item number 2 in the graphic
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Old 09-22-2014, 01:39 PM   #9
Big Bamboo
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It looks like he has a hose coming from the front hole on the M/C. Is there another one on the side as well?
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Old 09-22-2014, 01:45 PM   #10
RVDan
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You can buy an inline hydraulic switch from wilwood and others, just need to tee into the line somewhere


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Old 09-22-2014, 02:10 PM   #11
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Think I am following you with that last post.

Okay that last post gave me some real clarity. It would seem by the the looks of the attached photo the gentlemen that built the bike used the front thread of the master cylinder for the cable that runs down to the calliper.

Would anyone know if the thread is the same for the bottom port as the front? there seems to be a nipple in mine. If I remove the nipple and replace it with a banjo bolt pressure switch I should be good to go.

Then connect one wire to the power and the other to the brake light?

Thanks again
Rick
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Old 09-22-2014, 02:14 PM   #12
silverhead
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Yeah, that was originally what sent fluid to the brake caliper. I'm looking at photos on max BMW's parts fiche to determine this. If your front brake is working how you want it, you could just hook up your pressure switch there.
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Old 09-22-2014, 08:07 PM   #13
phookajoe OP
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Success!!!

Thank you all for your help today. I was able to find the Switch.

For anyone else that is missing or has a dysfunctional Front Brake Pressure switch.... A 1977 Volkswagon Rabbit switch works like a charm! You can get them at any auto parts store.

I'll be back online after my next pay check.

Cheers
Rick
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