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Motorcycle Electrical System Resistor

Discussion in 'General Electronics Discussion' started by tedstruk, May 24, 2017.

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  1. tedstruk


    Jan 7, 2012
    My 1981 xs1100 has a resistor pack in a metal case, that connects between the kill switch and the fuse box . The resistor is connected inline, like kind of in parallel on both sends to the kill switch .

    I wired a different resistor in, just like the wiring diagram shows, and the kill switch does not work.

    I don't have the original, I think I tossed it in the trash when I was rebuilding the bike.

    I found the specs for the original resistor pack, and the one I replaced it with is close in resistance. like a few ohms (say the replacement is a 16 ohm and the original was said to be 14 ohms)

    I need the original specs of the resistor pack, and the Yamaha shop won't help, and can't get a replacement. I would hate to ruin the brand new rectifier regulator I just bought, it was kind of pricy.

    where could I get a new replacement one of these? does anyone know what I need in the pack? can I build one? could some one build one for me?
  2. Bluejets


    Oct 5, 2014
    Can you show the wiring diagram you have?

    I found one from a '78-'79 model but there are many variants (UK, Aus, USA etc. etc.)

    From what I can make out it is the pre-CDI with standard coil ignition and a run resistor (similar to Toyota cars and many others).

    Idea is to run an 8v coil (or coils) and power is fed to this in run mode via the resistor.
    During start, the resistor is bypassed to put 12v on the coil to give a better spark at startup.

    '78-'79 diagram shows resistor value at 1.5R 10W.

    Given that standard ignition such as this draws around 2A , I'd say the values I just showed are pretty close.
    i.e. @ 2A and 1.5R the voltage drop would be around 3 volt.
    Wattage would be 2*2*1.5 = 6watts.

    Your 16R would seem to me to be way to high.

    Attached Files:

  3. shrtrnd


    Jan 15, 2010
    I don't know anything about motorcycles, but your electrical system description sounds a lot like the one on an old 1977 Dodge van I had. In case it helps in a Google search, that resistor pack was called a 'ballast resistor'.
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