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Thread: Oil Pressure switch wiring and more

  1. #1
    getset
    Guest

    Oil Pressure switch wiring and more

    Hello, I just purchased a 78 R100/7, and it came with a few things that I would like to fix.

    First and foremast is the lack of an oil pressure switch. The previous owner removed it and plugged the hole with a bolt and washer. Not to mention the wire that is supposed to plug onto it seems to be missing. There is a brown wire running along the bottom of the frame on the left side, but any connector has been removed, and I am not certain what color the wire is supposed to be. It looks like the wiring diagram has it as either a brown and green wire, or a purple and green wire. (I can't tell in the clymer color coded guide). Can someone tell me what color the wire is supposed to be, and where it might be routed?

    The other wires I am not sure about are a pair, one is brown, and the other is yellow and red. They plug into the main harness right in front of the tank and then they are cut. I believe that the brown is a ground.I am not sure about the other but I think the yellow and red one is either for the clutch switch (what is that? does it allow you to start the bike in gear?), or the turn signal buzzer (Not sure what this is either. Does it actually buzz when the turn signal is on?)

    Any help is greatly appreciated.

    Cheers
    Josh

  2. #2
    Liaison 20774's Avatar
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    Josh -

    Great bike...I'm biased, of course.

    Here's a reasonable color image of your wiring diagram. Check out the main page for everything 1978.

    http://www.omnilex.com/public/bmw78/78r100wire.jpg
    http://www.omnilex.com/public/bmw78/

    The diagram says the oil pressure switch wire should be brown with a green stripe. Check to see if that's what you have. You could also ohm out the wire up to one side of the oil pressure light in the instrument pod. As you can see from the diagram, the correct wire just creates a path to ground for the circuit. There's power on one side of the bulb...if the other side (ie, the switch) closes, then the light lights indicating no pressure. You really should have the oil pressure switch back in the circuit. If it comes on while you're riding at speed, you'll probably toast the engine before you could stop it. But if it comes on just as you turn the key and doesn't go off immediately after the engine starts, you still have time to shut down and figure out what's wrong.

    As for the other wires, check the diagram. I don't see a red/yellow wire. The clutch switch should be brown/yellow (and yes, the clutch switch allows you to start the bike in gear with the hand lever pulled in).

    There is a turn signal buzzer...the wires seems to be blue and blue/red. The buzzer is located somewhere under the left sidecover.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  3. #3
    getset
    Guest
    Thankyou for the info. I think the yellow/red wire is indeed yellow/brown. I am slightly color blind so reading some colors becomes a bit of a guessing game at times. I should be receiving a new switch shortly, and will check on the assumed wire. I know it is brown, but will have to borrow a pair of better eyes to see if there is a green stripe.

    regards,
    J---

  4. #4
    535IS
    Guest

    Brown is ground

    All solid brown wires on BMWs (cars or bikes) are ground.

  5. #5
    getset
    Guest
    Okee Dokee,

    Well I put in a new oil pressure switch and nothing, so I guess I need to start tracing that wire back. When investigation the wiring I have come accross a few other things.

    It looks like there is supposed to be a relay by the turn signal buzzer. There is a multi-pin connector, but no relay. Is this correct? Do I need a relay?

    Someone wired a switch to turn the headlight off. I removed that so it comes on with the key like intended. However, There is a yellow wire from the headlight which isn't connected to anything. Not sure what that does?

    Another odd item is that the wire from the run/off switch is connected directly to another wire of the same colors (Blue and green). Are those supposed to connect to the circuit board? Is there a diagram somewhere that illustrates where the wires attach to the board (i.e. which wire goes on #31).

    Thanks again for any help.

  6. #6
    Liaison 20774's Avatar
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    Quote Originally Posted by getset View Post
    It looks like there is supposed to be a relay by the turn signal buzzer. There is a multi-pin connector, but no relay. Is this correct? Do I need a relay?
    Yes, according to the diagram link provided above.

    Quote Originally Posted by getset View Post
    Someone wired a switch to turn the headlight off. I removed that so it comes on with the key like intended. However, There is a yellow wire from the headlight which isn't connected to anything. Not sure what that does?
    According to the wiring diagram link provided above, there is a yellow wire in the headlight shell. Is that the one you're talking about?

    Quote Originally Posted by getset View Post
    Another odd item is that the wire from the run/off switch is connected directly to another wire of the same colors (Blue and green). Are those supposed to connect to the circuit board? Is there a diagram somewhere that illustrates where the wires attach to the board (i.e. which wire goes on #31).
    Did the wiring diagram link provided above help? What circuit board are you talking about? There's a board inside the headlight...not relay a circuit board but a junction board for fuses and other wires.
    Kurt -- Forum Liaison ---> Resources and Links Thread <---
    '78 R100/7 & '69 R69S & '52 R25/2
    mine-ineye-deatheah-pielayah-jooa-kalayus. oolah-minane-hay-meeriah-kal-oyus-algay-a-thaykin', buddy!

  7. #7
    getset
    Guest
    Yes thank you, the diagram did help. I hadn't noticed that it marks out where the junction board is. I assume the rectangle denotes the the board. hopefully those numbers coincide with mine and I will be able to determine where the yellow wire goes. My lights work except for my bright and dim switch seems broken.

    Someday the battle will be won.

    Thanks

  8. #8
    getset
    Guest
    I also noticed that the other wires in question (blue green) go to the board as well, and not just connected to eachother.

    I wish I had small hands with real long skinny fingers.

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