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I have a scooter with the battery disconnected for the winter. I have no experience with this, and I forgot how the wiring were before. I tried to look online, almost every place said there should be a red and a black wire, positive and negative respectively; and if there is a third smaller one, that should go with the positive.

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Here is what I have

The problem is there are indeed three wires, two thicker and a thinner one, but the colors are black and blue for the thick ones, and red/blue for the thin. I also read it can ruin the bike if I connect it the wrong way... How should I connect this up without having any tools to measure? This is an italian bike, if that helps with anything.

  • Welcome to the site. You say an "Italian bike" ... this leaves a lot of room for error. Could you narrow down exactly the "bike" (or scooter) you are talking about? What make/model/year/engine is the scooter? – Pᴀᴜʟsᴛᴇʀ2 May 23 '17 at 12:09
  • @Pᴀᴜʟsᴛᴇʀ2 It is I believe a 2006 Malaguti F12, air cooled, with a carburetor. – Innkeeper May 23 '17 at 12:10
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You could read continuity between each wire and a known point in the circuit, such as the starter motor relay (if present) for positive and the frame for negative. If you see continuity between the wire and starter you know it's positive, if you see continuity between wire and frame, it's negative.

  • Thanks, it does have a starter, I just thought this would be more trivial so I don't have to take the body apart to trace wires. – Innkeeper May 23 '17 at 12:13
  • You could always look for a manual online first, too. If you could get ahold of a wiring diagram that'd be ideal but it might also be in the owner's manual – Ceshion May 23 '17 at 12:19
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Make yourself a very basic meter using a bulb. You can even use one from the vehicle itself.

Either that or trace the wires back to their origins.

It is fairly safe to assume that in most negative earth applications, wires with fuses are +ve.

  • Sorry, you mean kickstart the bike and see what's positive by connecting a bulb both ways? Also would it even spin starter with the polarity reversed? Can I just check by wiring in and see which way works? Or would that cause damage even without the engine running? – Innkeeper May 23 '17 at 12:49
  • I think the way he might have meant would be to wire a battery to a bulb with a lead on each end, then when the bulb lights there's continuity. It's a way to accomplish what I said without a multimeter – Ceshion May 23 '17 at 12:52
  • @Ceshion Wouldn't that only tell me which is positive and negative end of the battery? – Innkeeper May 23 '17 at 12:55
  • think of it like this: o-----(-/+)-----(bulb)------o where when you connect both leads to a continuous path, the bulb will light. I'd recommend a 9v battery – Ceshion May 23 '17 at 13:42

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