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What happens when you turn your key on.

Discussion in 'The Garage' started by XSLeo, Jun 19, 2011.

  1. XSLeo

    XSLeo XS650 Guru Top Contributor

    I have explained some of what happens several times. I thought maybe I should put it all together. I'll start with the early models, then explain the differences.

    When you turn the key on power flows from the battery positive through a 20 amp fuse to the key switch, the switch feeds this power out on a brown wire. This is the main power feed, the brown wire feeds power to the horn, regulator, brake lights and switches. The red/white wire feeds the engine stop switch, the blue wire feeds the tail light, the red/yellow feeds the headlight switch.

    I'll continue with the ignition circuit. Power flows out of the switch on the red/white wire to the kill switch, turn on the engine stop switch and power flows on the red/white wire to both coils. After the coils power flows to the points and condensers, now as you kick the engine over the points open and close. When the points are closed power flows through one of the coils, one coil is for the right side and one left. This power flow in the primary half of the coil builds a large magnetic field around the coil.

    When the points open this field collapses. This collapse creates a large voltage in the secondary half of the coil, this large voltage is what jumps the gap of the spark plug. Then the gas/air mix in the cylinder fires and burns, making the engine run. The points, being two sets, with a single lobe cam alternately fire on each side.

    Now the brown wire feeds power to the regulator. When you turn on the switch power flows out the brown wire to the regulator. At the regulator if this power is below the regulators preset voltage of 14.5 volts the regulator sends power out on the green wire and this goes to one of the alternator brushes. The power flows through the brush, into the rotor and out the other brush to ground at the stator housing, then along a black wire into the harness.

    This flow of power creates a strong magnetic field around the stator. Now as you start the engine the spinning rotors magnetic field excites the stator. This excitement causes the stator to create an AC voltage. This AC voltage travels out the three white wires to the rectifier. The rectifier changes the AC voltage to a DC voltage to charge the battery.

    As the battery charges, the voltage climbs, when it climbs to the preset 14.5 volts the regulator turns off the power to the rotor, the magnetic field stops, the stator stops making AC voltage/current and the battery stops charging. Now as the battery isn't charging the voltage drops, at 14.5 volts the regulator starts the charge cycle over again. The regulator does this hundreds of times per second.

    As far as the rest of the electrics go, it's pretty simple. The horn power on the brown wire flows through the horn to the button, where it gets grounded to toot the horn. The lights are simple, power to the switch, the switch turns on the lights. The turn signals are a bit more complicated. Power to the flasher then to the switch, then to the signals.

    When they added the starter they added a safety relay. When you turn the key on, (engine stop switch must be on), power flows to the starter relay through the safety relay. When the engine isn't running the safety relay is not powered, this lets power flow to the start button, the start button sends power to the start relay, witch in turn sends power to the electric starter. This cranks the engine. Then as the alternator starts to charge, a voltage is sent out on the yellow wire to the safety relay. This voltage switches the relay to stop sending power to the starter button, this disengages the starter and keeps the starter from working while the engine is running.

    They changed the system a bit in 74 or 75. The power didn't go to the starter button but to the start relay, then to the start button, where the button grounded the circuit to crank the starter.

    They added things to some of the systems. Mostly safety features, self canceling signals, clutch and side-stand switch's and relays to prevent starting in gear and riding with the side stand down.

    In 80 they made a couple major changes to the bikes. They swapped the points for an electronic ignition. The TCI, (Transistor Controlled Ignition). As in the older system when the key is on, and engine stop switch is on, power goes to the coil, It also goes to the TCI box. After the coil, power flows back to the TCI box. There is also a pair of pickups in a small black oval on the stator that gets triggered by a small magnet that is in-bedded in the charging rotor.

    Now as the engine turns this magnet passes the pickups. The pickups read the magnetic field of the magnet in the rotor and send signals to the TCI box. The TCI box uses these signals to know the crank position and the engine rpm's. The TCI box uses these signals to tell when the spark plugs should fire. When the TCI figures out when to fire the plugs, it turns a transistor on and off to turn the coil on and off, the same as the points did. The TCI being solid state has no moving parts to wear out so it doesn't need the constant adjusting and replacements that points do.

    They also redesigned the charging system. They went to a solid state combo reg/rec. This new reg/rec works similar to the old reg and rec but has a few changes. Now as the key is turned on, power is sent out on the brown wire to one of the brushes, as well as the regulator, The new regulator reads just the battery voltage on the brown wire. When the reg reads a low voltage it turns on a transistor. Power flows on the brown wire to the brush, through the rotor and out a green wire to the regulator. When the transistor is on, it grounds the green wire, this creates the magnetic field in the rotor causing the stator excitement and production of the AC current, the AC current is sent to the rectifier and as in the old system, changes to DC current and charges the battery.

    When the battery voltage reaches the preset 14.5 volts the reg turns the transistor off...power stops....no charge....voltage drops. Then repeats, the same as the old style. The solid state Reg/Rect can cycle much faster than the old mechanical reg, thousands of time a second......... Also no moving parts to wear out.
    These changes to the system greatly reduce maintainable and greatly increase the reliability of the bikes.

    If you can grasp these basics of how the systems work, then you can fix malfunctioning systems, and keep working systems working.

    A link to some Colored Wiring Diagrams., Jayel's album

    Thank you for taking the time to read this, hope it helps.
  2. XSLeo

    XSLeo XS650 Guru Top Contributor

    I would like to thank everyone who helped get my very rough draft into it's current form.
    Again Thanks for all the help with this.
  3. Shiffty

    Shiffty Jim Wilson

    Good info. Thanks for laying it all out for us.
  4. swbill

    swbill Slacker garage shop

    I see a sticky for this one. Great write up Leo
  5. XSLeo

    XSLeo XS650 Guru Top Contributor

    I didn't get into the lighting much, I haven't quite got all the stuff involved with that straight in my head, when I do I'll try to write that up too.
    If you can get your head around this then you can get a bike to run and charge. That's #1 on these bikes, lighting and the horn are simple compared to the charging system.
    Those are mostly add a fuse, run some wire and it works.
  6. jmink427

    jmink427 XS650 Junkie

    I don't get it.... Could you explain it again?..:D Lol.
  7. retiredgentleman

    retiredgentleman XS650 Guru Top Contributor

    Leo, that's a great explanation.....................so, from now on, we should not be getting any questions on electrical problems:D
  8. angus67

    angus67 Welder's penetrate deeper!!

    yeah, right.....:laugh:
  9. Excellent write up! :thumbsup: This should help a lot of people understand those wiring diagrams a little better.
  10. Bump...Bump....& Sticky for Leo's Basic XS 650 Electrics. "What Happens When You Turn The Key On"
    Last edited: Jun 23, 2011
  11. I'll add it to the tech page soon.
  12. littlebill31

    littlebill31 Smells of Raw Fuel

    Awesome Leo!!! Great stuff!!
  13. MAndrade1980

    MAndrade1980 XS650 Enthusiast

    Such a great post! From someone jumping into the world of xs650's with no experience this is a great help.
  14. racerdave

    racerdave ^ Gone not forgotten ^

    Leo, I cut your post to only ask what I need. What voltage does that relay turn on at, to keep the starter from re-engaging? Can I replace that starter safety relay with a Bosch relay like this: [​IMG]

    This is getting back to my post earlier this week, the oem setup is too big for where I want to mount it. The headlight wiring I'm not concerned with.
  15. retiredgentleman

    retiredgentleman XS650 Guru Top Contributor

    A 12 volt automotive relay should work except for one thing. The voltage on the yellow wire is AC voltage. Since the automotive relay operates on DC, the relay might "chatter". A diode in series with the relay might work to rectify the AC to DC voltage.
  16. XSLeo

    XSLeo XS650 Guru Top Contributor

    The stock safety relays could be adjusted for the voltage that tripped the relay. Up to the 78 When they went to the dual cover relay. One half was safety relay the other half turned on the headlight. They are not adjustable.
    The early relays should trip at 2.5 to 4.5 volts. On them ac or dc trips the relay. I use three aa batteries with short wires soldered on and in series. Two batteries is about 2.5 volts, three are 4.5 volts. I adjusted mine by changing the spring tension on the contacts. I adjusted the spring tension lower and lower till the 4.5 volts wasn't quite enough to trip the relay but the 2.5 volts would.
    The voltage on the yellow wire I think is more of a pulsating dc rather than a true ac. I have done some testing on the lighting relays as shown. The yellow wire will trip them.
    So yes it should work ok as a safety relay.
    Just did some testing with batteries. It took 5 batteries in series. Fresh batteries at 1.6 volts each, 4 won't trip, 6.4 volts, trips with 5, 8 volts.
    So the engine may over run the starter a bit on start up. This little over run will still be faster than your thumb releasing the button. It will also prevent the starter from working when the engine is running. As in accidently pushing the start button and having the starter try to engage.
    The four wire relays won't work you need the five wire relays. The four wire the relay just turns on a circuit. terminals 30 and 87. To use as a safety relay you need the 87A terminal this is on when no power then turns off when powered.
    Last edited: Dec 5, 2011
  17. phil meiste

    phil meiste XS650 New Member

    hey there, im like alot of 1st time builders out there who knew very little about bikes but thought that a simple tear down weld on a hard tail would be easy enough well a year and a half later and im finally getting her back in 1 piece, the thing is idk what wireing harness to get a 6pin or 8 pin? or how to get the headlights and brake light wireed in. Im not using signals on this build so all i need is to wire the stock headlight and a modle A tail light to work but electricle is greeke to me, anyone know where i could find that info?
  18. 650Skull

    650Skull SSSSSSSSSlither Top Contributor

    Go to the top of the page to the orange bar and click on the Tech link. Scroll down to electrical and the first link is XS650 wiring diagrams: "some wiring diagrams" There are pages of diagrams in different forms. full semantics to bare minimun
  19. rayth

    rayth XS650 Member

    HI Gents
    Have Mikes electronic tacho and Boyer Ignition - am unsure where to tap the signal wire into the jesus box/coils
    Has anyone done this please ?
    Appreciate /thanks

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