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Head light wont turn on when bike is started

Discussion in 'The Garage' started by Greg, Jun 25, 2016.

  1. Greg

    Greg XS650 Enthusiast

    image.jpeg
    I have a 81 special when started the light won't come on ,the charger is working, rld is working,when the key is on I get no light on speedo or tachometer the bike starts but the starter grinds a bit after start and head light won't come on and the head light warning light won't come on I believe the safety relay is shot but I'm not sure how to check it ,I can get the light to come on if I jump a wire from the positive terminal to the blue /black and blue/ yellow on the rld every thing else is working , can someone please confirm that when key is on should I have tachometer light don't remember if they should be on or not.also how do I check the safety relay

    Thanks in advance
    Greg
     
  2. 5twins

    5twins XS650 Guru Top Contributor

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    According to a wiring diagram for your model, the tach and speedo illumination bulbs are also controlled by the safety relay. They won't come on with just the key. The tail light and license plate light are the only ones controlled by the key. Have you verified that the bike is still charging? I ask because the yellow wire from the alternator sends voltage to the relay and triggers it once charging starts. No charging - no signal - no headlight.

    It's also possible that if you still have the reserve lighting unit installed, it has failed. Most of us remove them to avoid this problem. It requires that you jumper two wires in the harness plug. Here's how .....

    http://www.excess650.co.uk/tips & tricks.htm
     
    Greg likes this.
  3. Greg

    Greg XS650 Enthusiast

    Thanks 5twins the charger is working when I rev the engine I get about 14 volts at the battery ,I checked the rld according to a post that retired gentleman i believe posted and it appears to be good also . I tried to bypass the rld to no avail .do you know if there is a way to test the relay in the picture
     
  4. retiredgentleman

    retiredgentleman XS650 Guru Top Contributor

    Measure the AC voltage on the yellow wire and black wire at the Safety Relay.
     
    Greg likes this.
  5. Greg

    Greg XS650 Enthusiast

    Thanks retired gentleman I'm getting voltage when I test between the yellow and black is it safe to say that the part of the relay is not functioning
     
  6. retiredgentleman

    retiredgentleman XS650 Guru Top Contributor

    How much AC voltage are you getting? You should see about 14 volts AC at 1200 rpm.

    If you find 14 volts AC present, next step would be to measure the resistance between the yellow and black on the safety relay. resistance should be 21 to 26 ohms.

    Power comes from the headlight fuse on a red/yellow wire. When you turn the key on, do you measure battery voltage at the red/yellow wire?
     
    Greg likes this.
  7. Greg

    Greg XS650 Enthusiast

    get 14 volts AC when idling

    12 ohms resistance on black and yellow with key off

    And 12 volts DC with key on between black and r/y

    Now I'm confused I would think that less resistance would make it work
     
  8. retiredgentleman

    retiredgentleman XS650 Guru Top Contributor

    12 ohms resistance on the black and yellow, means the Safety Relay coil is partially shorted out. Therefore the coil cannot develop a strong enough magnetic field to operate the contacts. You need to get a used replacement Safety Relay.
    Put an add in the classified. Ask the seller to measure the resistance from yellow to black.
     
    Greg likes this.
  9. Greg

    Greg XS650 Enthusiast

    Thanks you so much for the information I've had it posted for a few days , I'm a dummy when it comes to electronic components and I try to find information on the threads before just asking, I'll report back when I find one
     
  10. Greg

    Greg XS650 Enthusiast

    On the road again,it was a bad safety relay.
    Thanks retiredgentelman and 5twins ,it's members like you that make this forum so great by helping out and offering your vast knowledge to solve problems and make it easy to understand .
    I really can't thank you enough
     
  11. 5twins

    5twins XS650 Guru Top Contributor

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    Glad you solved the problem and were able to get the part. Did you find it locally? I checked my stash and did have two, but one was broken. That left me with one spare, which I kinda like to have for myself, lol.But, I don't even use the headlight portion on my relay anymore. I unplugged it so I can control my headlight all the time with my handlebar on-off switch.
     
  12. Greg

    Greg XS650 Enthusiast

    You won't believe it but my neighbor races a drag bike and is a pack rat ,I showed him the relay he comes back about a hour later with one and says not sure why I would have one but try this and it worked he rides a Harley and races a Kawasaki the relay is very beat looking but it works he think it's from a 79
     
  13. Greg

    Greg XS650 Enthusiast

    Btw my bike only has a hi/low switch
     
  14. 5twins

    5twins XS650 Guru Top Contributor

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    Parts is parts, lol. Yes, '78 was the last year to have the handlebar headlight on-off switch.
     
    Greg likes this.
  15. 5twins

    5twins XS650 Guru Top Contributor

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  16. Grimmith

    Grimmith Samurai

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    So does this mean the bike has to be running for the headlight to work? I'm having the same exact issues currently. Other than needing a new rebuild kit for the carbs, I got the turn signals to work but no HL. so if I just need the bike to run for the HL that would be awesome
     
  17. XSLeo

    XSLeo XS650 Guru Top Contributor

    Your headlight comes on but no high/low? that could mean the bulb is bad. Easy to check. It only takes two screws to get the headlight out. On the plug that goes on the headlight trace the wires back into the harness. You will find these plug in. Unplug at these places.
    Now you should have the headlight with plug and some wires in your hand. The black wire is ground. The green is low beam, yellow is high. use jumper wires, hook the black to battery ground. Hook one jumper to battery positive, touch this jumper to the green and yellow wires. Do both beams light up? If so bulb is good. Now you need to take the left side switch housing apart to check the wires on the high/low switch. One may be unsoldered or the switch itself is dirty. You can take the switch out of the housing to clean it. Bright shiny contacts are a good thing.
    There may also be a poor connection in the wiring somewhere between the switch and headlight.
    Leo
     
    GLJ likes this.
  18. fredintoon

    fredintoon Fred Hill, S'toon. Top Contributor

    Hi Grimmith,
    if your HL don't mean "Hi/Lo" but means "headlight" yes.
    Once the safety relays see current from the alternator (even if the engine don't start at that time) one of them locks out the E-starter and t'other one turns on the headlight.
     
    Last edited: May 4, 2019
  19. 5twins

    5twins XS650 Guru Top Contributor

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    But the bike doesn't necessarily need to start. Sustained cranking and spinning the alternator rotor enough to start generating some current is often enough to trip the relay before the engine starts.
     
  20. fredintoon

    fredintoon Fred Hill, S'toon. Top Contributor

    Hi 5T,
    I'd say "sometimes" rather than "often" but yes, that can happen. I will edit my post to say so.
     

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