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Thread: How to test the starter relay (also, is this even the right relay?)

  1. #1

    How to test the starter relay (also, is this even the right relay?)

    We're on a road trip on a 1973 R75/5 LWB and we rode in heavy rain yesterday. After I turned off the bike it wouldn't start again. Nothing happens when I push the starter but I can kick start the bike. I let it dry over night and same issue. There's no sound at all (no solenoid clicking) and the lights don't dim. Measuring the battery while pressing the starter shows no dip in voltage.

    Jumping the black wire on the starter relay to the battery positive cranks the starter so I know the solenoid and starter works. Duane Ausherman has a great post for identifying starter problems (https://w6rec.com/electric-starter-troubleshooting) but my bike isn't wired like that. The starter/turn signal switch wires are fed straight through the headlight bucket to the main wiring harness so I can't short the ground without cutting the wire. I tried shorting the brown/black wire on the starter relay to ground but that doesn't crank the engine which leads me to suspect the starter relay rather than the ignition switch/wiring.

    I popped open the relay thinking maybe it just needed to be cleaned but it looks pristine, and it also doesn't look like the pictures of r75/5 relays I can find online.
    IMG_20191116_203016.jpg
    IMG_20191116_203024.jpg
    IMG_20191116_203035.jpg
    Any clue how I can verify that the relay is the problem?

    As I'm on the road I may have to just circumvent the relay for now but I'd prefer to fix it properly right away.
    1973 R75/5

  2. #2
    My hunch is that the problem is with the starter switch. I would, as best as possible, work WD40 spray into the switch to clean and dry it out.
    Paul Glaves - "Big Bend", Texas U.S.A
    "The greatest challenge to any thinker is stating the problem in a way that will allow a solution." - Bertrand Russell
    http://web.bigbend.net/~glaves/

  3. #3
    Registered User Guenther's Avatar
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    When you put GND on spade #85 and 12V on spade #86 on the relay the contacts should close with a click. If there are no numbers at the base of the relay:

    #85 receives the blue/yellow wire from the starter switch (GND)
    #86 receives the blue/green line from the kill switch (12V)

    You can check the starter switch by connecting the blue/yellow wire to one side of a bulb and the other side of the bulb to #86 (with ignition on) or, use a voltmeter instead of the bulb to see ~12V.

    Also #87 a black wire goes to the starter solenoid. When you connect this wire to 12V the starter should turn.

    /Guenther
    Last edited by Guenther; 11-17-2019 at 05:08 AM.
    2017 F700GS

  4. #4
    Registered User bandersnatch's Avatar
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    The starter relay on my 75 R90/6 did exactly the same thing. One day it's working, the next nothing, no clicks, no start, no voltage drop and it runs fine shorting across the starter terminals.

    If you want a true test, go to Autozone or Napa and buy a Bosch relay like Motoraad Elektrik sells for $10 (sorry, I don't have the part number handy, hopefully someone else can supply that). If it starts the bike, you can either leave it as is or go ahead and buy a replacement relay.

    If I were a betting man I'd put money on it being the relay. And if not, at least you have a spare for when it is . . .

    Best of luck,
    Larry
    Last edited by bandersnatch; 11-18-2019 at 08:37 PM.
    Bandersnatch
    Larry Wheeler, Hillsboro Oregon
    1975 R90/6 built 9/74

  5. #5
    Quote Originally Posted by Guenther View Post
    When you put GND on spade #85 and 12V on spade #86 on the relay the contacts should close with a click. If there are no numbers at the base of the relay:

    #85 receives the blue/yellow wire from the starter switch (GND)
    #86 receives the blue/green line from the kill switch (12V)

    You can check the starter switch by connecting the blue/yellow wire to one side of a bulb and the other side of the bulb to #86 (with ignition on) or, use a voltmeter instead of the bulb to see ~12V.

    Also #87 a black wire goes to the starter solenoid. When you connect this wire to 12V the starter should turn.

    /Guenther
    Thanks for.the detailed reply.

    There are no numbers on the relay and I don't have those cable colors. I have these wires:

    1 cold red & 1 hot red connected to the same contact.
    1 cold blue & 1 hot blue connected to the same contact.
    1 green/black green that's hot when the ignition is on.
    1 black that goes to the solenoid (which I can jumpmto fire the starter)
    1 brown/black that's 1.36V with ignition on and 0V when pressing the starter button.

    The fact that the black/brown drops to to 0 when pressing the ignition switch is what leads me to believe that the relay is broken. I'm not sure if 1.36V is normal though.

    So to test the relay I should have the rest hot wire connected and the green/black wire connected hot, then ground the brown/black wire right? With everything connected if I ground the brown/black then nothing happens (no audible click from relay).
    1973 R75/5

  6. #6
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    The starter button in on the ground side of the relay so it grounds the relay coil to complete the circuit. I would assume the brown/black wire goes to the switch. The 1.36 volts is not right, it should read battery voltage and then drop to zero when you push the starter button.

    Does the large red wire have battery voltage all the time? Even with the starter button pushed?

    Does the green/black green that's hot when the ignition is on stay hot, full battery voltage, when the stater switch is pushed?

    This might help,

    http://5united.org/articles/wiring/72fused.jpg
    From the only real Fargo, ND!

  7. #7
    Quote Originally Posted by PoorUB View Post
    The starter button in on the ground side of the relay so it grounds the relay coil to complete the circuit. I would assume the brown/black wire goes to the switch. The 1.36 volts is not right, it should read battery voltage and then drop to zero when you push the starter button.

    Does the large red wire have battery voltage all the time? Even with the starter button pushed?

    Does the green/black green that's hot when the ignition is on stay hot, full battery voltage, when the stater switch is pushed?

    This might help,

    http://5united.org/articles/wiring/72fused.jpg
    The red and the green/black stay at battery voltage with the starter pressed.

    If the ignition switch wire is supposed to be battery voltage then is the relay just there to switch ground vs hot? That seems odd.
    1973 R75/5

  8. #8
    Liaison 20774's Avatar
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    The OEM part is 12 41 1 350 775. Basically, the g/b wire brings 12v into the relay on a smallish wire...terminal 15...I think 31b is the ground path for this 12v (brown/black wire). Once the button is pushed, this 12v engages the internal relay and connects voltage into the relay at #30 (red wire) to the black wire #87 which runs out to the starter solenoid. That voltage pulls down the relay in the solenoid which then connects a very large black wire from + battery...the starter is grounded.
    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!

  9. #9
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    Quote Originally Posted by jakobw View Post
    The red and the green/black stay at battery voltage with the starter pressed.

    If the ignition switch wire is supposed to be battery voltage then is the relay just there to switch ground vs hot? That seems odd.
    Sounds like a bad relay to me.
    From the only real Fargo, ND!

  10. #10
    Another reading showed the brown/black wire at 12 volts so yeah, definitely the relay. For now I'm just going to bypass it as I only have a few days left on the trip and I'll go ahead and order a replacement.

    Thanks for all the help!
    1973 R75/5

  11. #11
    Registered User Guenther's Avatar
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    I found a better /5 diagram which shows a transistor in the relay. HITEK!

    The transistor is used to energize the relay and I guess it is shot.

    Euromotoelectrics.com has the relay for $70 (HITEK price).

    /Guenther
    2017 F700GS

  12. #12
    Rally Rat 1074's Avatar
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    Quote Originally Posted by Guenther View Post
    When you put GND on spade #85 and 12V on spade #86 on the relay the contacts should close with a click. If there are no numbers at the base of the relay:

    #85 receives the blue/yellow wire from the starter switch (GND)
    #86 receives the blue/green line from the kill switch (12V)

    You can check the starter switch by connecting the blue/yellow wire to one side of a bulb and the other side of the bulb to #86 (with ignition on) or, use a voltmeter instead of the bulb to see ~12V.

    Also #87 a black wire goes to the starter solenoid. When you connect this wire to 12V the starter should turn.

    /Guenther
    There is no blue/yellow wire on a /5 harness! You have a green/black wire that powers the relay with the ignition on. A brown/black wire goes to the connection block ion the headlight where it connects to a brown/black wire going to the handlebar switch. Pressing the start button grounds this wire.
    So. First, ground the terminal where the brown/black wire goes on the relay. If nothing happens then the problem is in the relay since you have already eliminated the black wire that goes to the solenoid.
    If the starter turns when you ground the terminal then the problem is between the relay and the switch. Go to the terminal block in the headlight and ground the brown/black wire on the relay side of the connection block. If the starter turns then ground the switch side. Not turning the starter indicates that there is no connection within the connection block. Not very common. If the starter turns then it is the switch.
    There are those who will tell you to take the switch apart and clean it. This accomplishes two things. You will become totally frustrated as this job is a real PIA which may or may not fix it. And besides, it is an old switch! The other thing is that if we all keep repairing these switches then I suspect that the factory won't see the need and quit making them. Just my opinion. The cost of a new switch is just the peace of mind that the new switch will probably last another 40 plus years.
    I'll get off my soapbox now.
    t
    Boxerbruce

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