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Safety relay question

Discussion in 'The Garage' started by Grinder, Feb 19, 2010.

  1. Grinder

    Grinder XS650 Guru

    Hello, I'm trying to replace some of the 30+ yr. old electrics on my 77 with some more modern stuff. The safety relay get's energized from the yellow wire comming from the stator. This current isn't really true AC or Dc from what I understand so I'm not sure what kind of relay to replace it with. The bike isn't running right now so I don't even know how many volts the yellow wire has with the bike running. Any help would be appreciated.
  2. inxs

    inxs xx

    - not exactly sure but i think the safety relay has power in from the battery through the red wire...what i think the yellow wire from the alternator does is open the relay preventing you from being able to start the bike while the alternator is running...the red/white wire is the power feed to the solenoid...ie the relay power feed in is red, power out is red/white and the yellow opens and closes the relay

    - seems to me that its kind of difficult to not know the bike is running and the normal function of the solenoid and starter button basically does the same job...when i was running e-start, which i dont any more, i removed the safety relay altogether
  3. Grinder

    Grinder XS650 Guru

    The yellow wire does activate the relay by opening the contacts as soon as the bike starts and killing the power to the starter relay. It's probably not a bad idea but not really necessary either. It just prevents the starter from being accidently engaged when the motor is running. Most all cars have this feature I believe.

    The stator is threee phase and the yellow wire comes from a seperate portion of it from what I've heard. The voltage comming from it isn't truely AC though I guess. Dc voltage seems to activate the stock relay which seems odd but I can't test the yellow wire without the bike running.
  4. yamaman

    yamaman xs650 addict

    This is just guess work really, but if you wanted to make your own safety relay, maybe this way would work:
    As far as I know, the yellow wire is un-rectified & un regulated. So if you ran the yellow wire to a bridge rectifier, then to a 24v DC relay (normally closed), you would possibly be safe.
    It is possible to run a DC coil (relay in this case) on AC & vis versa. There are though differences in how each is made. And you may well have reliability issues with running the wrong coil.
    So for starters, you need some kind soul to measure the voltage on the yellow wire, and see how far it increases as the engine is reved, perhaps a 12v relay will do, or perhaps there is not enough voltage to run a 24v relay???????
  5. Grinder

    Grinder XS650 Guru

    I did try hooking a standard 12V auto type relay to household AC (6 and 12V) and it just buzz's. We have a regulated AC power supply at work so I tried it. The current comming out of the yellow wire isn't true AC though form what I've heard.The stock relay does seem to work on 6 or 12V DC however, so maybe a standard 12V relay would work.
  6. XSLeo

    XSLeo XS650 Guru

    I have checked regular lighting relays on my bike. The yellow wire supplys enough voltage to work the relays without any extra parts. I have also checked the voltage on the yellow wire. I don't recall the exact voltage, some where around 10 volts. In my factory manual it lists the safety relay as having a cut out voltage of 2.5 volts. This means that once the yellow wire voltage hits 2.5 volts the safety relay shuts the starter off.
    It does this to help prevent damage to the starter gears from holding the start button after the bike starts. Yes, you may have a quick thumb, it's not as quick or as consistant as the safety relay.
    I have a 75, the wiring stock wiring is very close to the 77. I have rewire the bike. I have been thinking about using a safety relay from a later model. The ones that turn the headlight on. I would use it with a resistor to turn on the low beam of the headlight at a reduced output, as a daytime running light.
    The 75 has an on off switch for the headlight. I find myself running around with out my headlight on. With the safety relay turning on the low beam as a day time running light, even dimly lit will be better than no light. Then when I turn the headlight switch on the headlight would work as normal. Like for night riding.
    You could use a regular lighting relay to do the same thing.
  7. xjwmx

    xjwmx XS650 Guru

    Here's someone's schematic.

    The text describes what you have to do to copy the function.

    Last edited: Sep 14, 2010
  8. XSLeo

    XSLeo XS650 Guru

    The yellow wire maybe a pulsing dc. When the voltage reachs 2.5 volts the relay trips. Even as the dc pulses on the yellow wire as long as the average of the pulsing stays above the 2.5 volts the relay stays tripped.
    I don't know much about how the lighting half of the relay functions. If you use a regular lighting relay to turn the headlight on. The yellow wire provides enough voltage to hold the relay on. This will work ok. If the bike stalls, the light goes out.
    On the stock relay it stays on when the engine stalls.
    I assume that once the relay closes the lighting side power on the red wire is fed through the resister to keep the relay tripped. The diode keeps the power from the lighting side from feeding back and keeping the starter side latched.
    If the bike stalls, the yellow wire stops suppling voltage so the starter side unlatches and lets the starter work. The diode keeps the lighting side power from keeping the starter side latched. Using the resister the lighting side stays latched. If the power fed back from the lighting side it would keep the starter side latched and you couldn't restart with out cycling the key off and back on.
    Once you turn the key off power is no longer fed through the resister and that side unlatches, turning the headlight off.
    Hey, I think I do understand how it works.
    So you start the bike, the headlight comes on, you drive off. Then you stall the engine, you just push the start button and the engine restarts. If when it stalls and you want to turn the headlight off before you restart, you need to cycle the key off and back on to turn the headlight off. Then you restart and the headlight comes back on.
    Thats how it's supposed to work. Right?
  9. xjwmx

    xjwmx XS650 Guru

    Yes. From the schematic if there's enough power from the yellow wire to hold SR on and at least trip LR, it works like it should and like you describe. I won't say anything further without looking at the yellow wire on a scope, which I'm not going to do ;)
    Last edited: Sep 14, 2010
  10. kenintn

    kenintn Uncle Ken

    The safety relay is actually a DC relay activated at around 6 volts, and stays in until volts created by the stator drops down to around 2-3 volts.

    Though the SR rarely goes bad the contacts do get corroded. If you suspect the relay is bad you can test it. More info can be found at:


  11. xjwmx

    xjwmx XS650 Guru

    The resistor and the coil resistance of LR make a voltage divider that means LR never sees more than about 6V either (ballpark). So both relays need to be 6 volt ones. The 47 Ohm resistor ought to be 1 Watt size or bigger.
  12. kenintn

    kenintn Uncle Ken

    FWIW the safety relay and lighting relay coils are connected parallel or across the voltage source from the stator coil. There is a resistor in the dual relay (Safety/Lighting Relay) that provides a back feed of voltage from the lighting fuse circuit through the lighting contact to the Lighting Relay's coil once the relays turn on. This back feed keeps the lighting relay on and the headlight on should the alternator stop charging. There is a blocking diode in the circuit going to the safety relay coil that prevents this back feed voltage from reaching it. Thus the safety relay drops out when the alternator fails.

    Yamaha later deleted this feedback circuit, I'm guessing they realized one would not want the headlight on drawing 4-5 amps from the battery with a dead alternator. :~)

  13. xjwmx

    xjwmx XS650 Guru

    Might ought to leave it in. If the alternator goes it's a simple matter to disconnect the headlight if you choose. But if you're leaned over in a turn on a mountain road in the dark and your headlight goes out it's a stickier problem :)
  14. Special welcome to (and very glad to see) another XS 650 guru checking in and participating and for what hopefully will certainly be some very knowledgeable contribution.

    Hi Ken Maxwell....very glad to see you joining us. Hope you enjoy us and like the site. Best wishes! Blue

    FWIMBW.....Ken is the author/marketer of the well known CD "The Yamaha 650 Wiring Explained......a keeper, for sure!
    Last edited: Sep 15, 2010
  15. xjwmx

    xjwmx XS650 Guru

    A long time ago I did something like Yamaha did if they deleted holding LR on. It wasn't a safety issue but could potentially cause expensive damage. I was working on this product that over the years had had features added and removed and changed and I realized that somethng I had recently done would cause that bad problem if a particular combination of events transpired....

    I verified that I was right, quickly came up with a fix, and went to the guy who hired me and told him about it, He called a meeting that included my boss and it was decided to have a recall. I don't know how many they recalled but they'd been shipping hundreds or maybe thousands a day for awhile. Some now installed and some sitting on a shelf somewhere. It's not easy - do you wait for something that night not happen or do you head it off. But if it's a safety issue there's no question. But I discovered I had a pretty good boss; his major complaint to me was that I first went to the guy that hired me instead of him. Maybe his feelings were hurt, or maybe he'd have preferred to sweep it under the rug :)
  16. kenintn

    kenintn Uncle Ken

    Thanks Blue. Always enjoy a good discussion.
  17. kenintn

    kenintn Uncle Ken

    Point well made. They should have dealt with the weak alternator system and beefed it up though they did raise the amperage output in later years (1980-81?). However, IMO they knew they had a problem before 1978 because they designed in a circuit that turned on the brake light if the alternator failed on the '78 models. Problem is they never bothered telling anyone in the owners manual (to my knowledge) that the alarm exsisted.
  18. Batman452

    Batman452 XS650 New Member


    I have installed an HID headlight on my '02 and in order to bet it to work properly am going to have to bypasss the Light Relay.

    After reading this thread and the one on the Headlight Relay, I have figured out that this can be accomplisehd by looping the "BL & RY" wires on this schematic.

    Any Thoughts?

    Attached Files:

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