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Thread: /5 electrical issue/starter button

  1. #16
    BeemerBoy terham's Avatar
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    With positive meter lead on br/bl pin in relay and negative meter lead on negative battery, 11.8 v goes to 12.3 v when starter button pushed. Pin for black wire stays at 12.3 v.

    So the starter switch is bad? It should go to 0 v when starter button pushed? I get the same readings (11.8 to 12.3 v when starter button pushed) at the two connections inside the headlight shell where the br/bl wire connects into and out of the connector block.

    I have a replacement switch. If I wanted to test this new switch without completely wiring it in, what are the minimum connections I would have to make to test if the new switch solves the problem? Would I have to connect more than the br/bl wire into the connector block and maybe the grounding brown wire with a spade connection?
    Terence
    R75/5 R100RS K100RS R1100S

  2. #17
    R100GS, '89 Guenther's Avatar
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    If I disconnect the brown/black wire that runs from the starter button into the starter relay (terminal 31b), and jump the male connection, the starter turns over.
    I assume "jump" means you connected batt+ to terminal 31b.

    The 75/5 diagram I am looking add (Haynes BMW Twins) shows the other end of the starter switch runs to a screw-on plate in the headlight box connected to screw #31. #31 then connects to frame. The "hightech" starter relay (1 transistor) acording to the diagram only closes the realy inside if 31b is connected to ground.

    So, I may look at the wrong diagram or, you have a "modified" 75/5 in this area.

    /Guenther

  3. #18
    R100GS, '89 Guenther's Avatar
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    I attached a test lamp ... wire from the starter button and the other end to the positive battery post. ...I turned on the ignition ... I press the starter button, the test lamp comes on.
    Pin for black wire stays at 12.3 v.
    This would indicate that the starter switch does connect to ground. With 12.3V on 87 (black wire) the starter solenoid should be energized.

    I am more puzzled.

    /Guenther

  4. #19
    Registered User lmo1131's Avatar
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    Okay, let's get on the same page.

    "It is what you discover, after you know it all, that counts." _ John Wooden

    Lew Morris
    1973 R75/5 - original owner

  5. #20
    BeemerBoy terham's Avatar
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    I have an unfused /5 so the lower diagram is the one I've been working from.

    By jumped, I mean I used a double alligator clipped lead and one clip was either on pin 31b (br/bl wire disconnected, all other relay connections maintained) or on disconnected black wire from pin 87 and when the other alligator clip was briefly touched to the positive battery, the started turned over in both situations.

    The relays I have are replacements and they don't have the pins marked anymore like the original did, but I'm 99.999% sure the relay is wired correctly. I'm calling things pin number whatever based on the wiring diagram and the color wire connected. Below is my starter relay. From left to right on outside pins of relay are blue (D+), red (30), green (15), from left to right on frame side of relay are brown/black (31b), red (30) and black (87).

    Terence
    R75/5 R100RS K100RS R1100S

  6. #21
    R100GS, '89 Guenther's Avatar
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    The old wire color nomination in german thinking...nature related:

    BR = brown (german "braun"), which stands for soil->earth->ground
    GR = green (german "gr??n"), which stands for plants->life->energy

    So any wire marked with "BR" or "BR - ?" should be connected to ground.

    Wire 31b is marked "BR - SW" (brown/black, german braun/schwartz) indicates it is connected to ground. To verify 31b disconnect the br/sw wire and measure the voltage between the loose end of the wire and batt+. Should read 12.3V with starter button pushed and 0V otherwise.

    Here's a diagram for the relay: http://www.bmwmoa.org/forum/showthread.php?t=61255

    /Guenther
    Last edited by Guenther; 11-22-2012 at 05:54 PM.

  7. #22
    BeemerBoy terham's Avatar
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    Thanks, I really appreciate this help.

    When connected to positive battery, the loose br/bl wire from 31b is 0 v and when I press the starter button, it's 12.3 v.

    I don't mean to beat a dead horse, but am I correct in my thinking that having the starter turn over when the black wire from pin 87 is connected to positive battery means the starter is OK and having the starter turn over when pin 31b is connected to positive battery means the relay is working? I thought having 12 v at the br/bl wire going to pin 31b when the starter was pressed meant the starter switch was also OK?
    Terence
    R75/5 R100RS K100RS R1100S

  8. #23
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    You do not have the right understanding of function.

    The starter button function is to connect through various wires terminal 31b on relay 8 to ground when the button is pressed.
    You can see clearly in the above diagram(no fuses) that within device 8 (starter relay) that 31b is the ground end of the fine wire coil forming the electromagnet within the relay. When this end of the coil is grounded the relay operates. When the ignition is on and engine is not running the other end of this magnet coil is "hot".

    When the relay operates terminal 87 which is connected to starter motor 50 by black wire is connected to terminal 30 which is "hot" when the ignition is on and the starter motor runs.

    You proved the starter motor works ok by connecting black wire from starter motor to battery pos and starter runs.

    I think you proved something is goofy when you connect any wire from 31b to the battery pos and that makes the relay actuate and the starter motor run. Connecting 31b to ground should make the relay actuate and the starter motor run.

  9. #24
    R100GS, '89 Guenther's Avatar
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    Terence,

    I agree with you that connection 87 is working "as expected" and the starter is good.

    But the starter button and the starter relay don't make sense. With - starter button connects to 12.3V and relay closes when 31b is connected to 12.3V - this obviously does not work, which all by itself doesn't make sense.

    Something strange: The picture you showed of your starter relay has one oddity: the mounting blade is on the "wrong" side. All other pictures I found on the net showed the 87 and 31b pin at the opposite side of the mounting blade.

    You said you replaced the starter relay? How does the one look that you took out?

    To check for one mystery: Have you verified the wire from the starter button into the headlight box for any damages and that it connects to the right srew which connects to ground?

    You do not have the right understanding of function.
    44006...only if the diagram is right.

    Terrence, did you ride through a voddo zone short before this all started?

    /Guenther

  10. #25
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    starter

    Install the new switch. I had a similar problem with my /5 and installing the new switch was the cure. What you don't see unless you take the swith apart is that there are two contact plates, a spring and some wires crammed into the swith. I was having a tempermental switch, poor starting and voltage loss when the bike was parked for a day or two. It would kill the batter dead in two days. After rebuilding the switch (which in itself is the devil's work due to the fact that the whole assembly is spring loaded) the switch was better but not much. I think the contact activation parts inside the switch get worn and the contact plates don't move as they should and then you get voltage loss through the worn contacts and poor or indirect contact when you try to press the button the activate the starter/relay circuit.

    Follow the wiring diagram - you have to go inside the headlight and pick up the circuits there. It's a bit time consuming, because you are also wiring the turn signals and ground but if memory serves me correctly you don't have to access the top side of the ignition switch (another real pain in the a**).

    The switch may look perfectly fine but it's probably toast and you really wouldnt think of testing it for current leakage though the other circuits within the switch.IMOH they're not really rebuidable.

    My experience, anyway.

  11. #26
    BeemerBoy terham's Avatar
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    The old "bad" relay and the new "good" relay are both BMW parts but don't have the pin numbers stamped on them, but when I replaced them, I only did one wire at a time and put them on the same pins so I wouldn't have a bunch of wires and wouldn't know where they went.

    Just to be sure, I switched the pins that the br/bk and black wires are attached to with no improvement.

    With the replacement "good" relay mounted and with what I think is a better understanding of how all this works, if I jump pin 30 to pin 87, starter turns over. I think this also shows the black wire is on the right pin. If I disconnect the br/bl wire at pin 31b, and ground the pin manually with a double alligator clip lead, nothing. If I ground any of the other pins besides 30 or 87, nothing happens, which I think also shows the br/bl wire isn't on the wrong pin.

    On either the "good" or "bad" relay I have, if I only connect the red power wires on pin 30 and the black starter wire on pin 87 (no connections at pin 31b, 15 or D+), the starter turns over when 30 and 87 are jumped, but not when 31b is grounded manually. I would think this eliminates any issue with the starter button itself and any wiring issues in the headlight. Neither relay seems to be closing when grounded.

    For now, I'll replace the rotor to fix the charging problem, and until I get the starter issue figured out, use the kick starter.
    Terence
    R75/5 R100RS K100RS R1100S

  12. #27
    R100GS, '89 Guenther's Avatar
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    Terrence,

    here is my final and then I let it go.

    I "think" your starter button is ok and we know the starter is ok.

    The problem could well be related to the problem with the charging system.

    Question: Does the "idiot" light come on when you turn on the ignition?

    If not then the (near) GND on D+ which connects to the transistor in the relay box cuts off power to the relay inside. There's a good chance that nothing was wrong with the starter system all the time.

    If the "idiot" light does come on I suggest a final test. This test opens the transistor without using D+:

    - remove the 2 blue wires from the starter relay
    - connect the two ends so the blue D+ wire now goes straight to the "idiot" light to still get a small current to the rotor
    - connect some GND to the D+ spade of the starter relay, this should open the transistor
    - turn ignitio on and press the starter switch

    If it fails to turn the starter then I have to assume the starter relay is the problem.

    Good luck!

    /Guenther

  13. #28
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    "Neither relay seems to be closing when (31b) grounded."

    This is as it should be - Gunther put it better - you also have to turn on the transistor to manually get this relay to trigger.

    I have one of these relays in hand with can off
    Pos bat to 15
    Gnd bat to D+ (this is what turns the transistor on)
    Then and only then will Gnd bat to 31b cause the relay to trigger

    If the D+ is finding ground through the alternator rotar when engine not running and your rotar is open then this is at least part of your problem

    Also as to the mounting blade - the guts will go in the can either way once the can has been pulled off so if either of your relays look like someone pulled the can off to clean the contacts then the mounting blade may be on the opposite side from BMW original mfgr.

    You may have two problems that ganged up on you
    1) your start button is bad - not making good contact - your spray did not reach its contacts (sounds like your long gradually worsening story)
    2) your rotar then failed open for other reasons (common with age) and this causes the transistor
    part of the relay not to function as intended

    Suggest test partly as Guenther suggested

    "- remove the 2 blue wires from the starter relay" (these are on the D+)
    "- connect some GND to the D+ spade of the starter relay, this should open the transistor"

    Remove wire from 31b
    Now with ignition on jump 31b to ground engine should crank - if it does the problem is
    the start button and/or its wires

  14. #29
    BeemerBoy terham's Avatar
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    Thanks everyone, this has been a big help to me.

    Quote Originally Posted by Guenther View Post
    Question: Does the "idiot" light come on when you turn on the ignition?
    The red light does not come on when the ignition is on. If I remove the wire from terminal DF on the alternator, turn on the ignition and ground the DF wire, the light glows, so the bulb is good. Following the testing outlined in Rick Jones' "Classic Boxer Charging" book, I concluded the rotor was bad. Though possible, I found it hard to believe that both the starter circuit and charging system could independently fail at the same time and was hoping I had only one problem.

    When the new rotor arrives, I'll put it in and report back. I will try that first, since for me, that is simpler than replacing the switch, because of all the other connections I have to make in a confined space. If it turns out to be the rotor, then I'll have a new switch, starter relay and voltage regulator to keep in hand for future problems.
    Terence
    R75/5 R100RS K100RS R1100S

  15. #30
    BeemerBoy terham's Avatar
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    Thanks for the help everyone. A big thanks to Radar41's 24/7 tech support.

    Got everything buttoned back up, adjusted the tire pressures and off for a road (rode?) test.
    Last edited by terham; 11-29-2012 at 05:35 PM. Reason: Correcting self-launching video
    Terence
    R75/5 R100RS K100RS R1100S

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