Q. Why is my scooter blowing fuses?
First off, never bypass a fuse!
It's there to protect you and your scooter. Bypassing a fuse or using a fuse with a higher rating can lead to failures of other components in the circuit, burning or melting wires and connectors, and can even result in a fire.
If your scooter is new to you, there's a possibility that someone installed an improper fuse into the fuse holder. Lower rated fuses may fail even when everything else is working properly. The main fuse for many scooters tends to be 10A to 15A. Check for any writing on your fuse holder or fuse block that may specify a rating or consult your scooter's owner or service manual before trying a different fuse.
Most commonly fuses blow because of an electrical short to ground, usually simply referred to as a "short". If you have a short, it means that somewhere in the electrical system a positive power source is making contact with a ground source. Positive sources could be a power wire or connection to or inside of a component. A ground source could be a ground or negative wire, the frame or chassis components, or engine. Pretty much anything metal attached to or touching the frame could be a ground that contributes to a short.
Use any available knowledge to narrow the focus of your search for the problem. For example, if the fuse always blows when you use the electric starter, check the electric starting circuit out first. Electric starting tends to put the heaviest load on the system, so it could also be an indicator of an improper fuse rating unable to handle the load. If the fuse blows when you hit the brakes, examine the brake light circuit. If the fuse blows as soon as you turn the key on, unfortunately it could be anywhere receiving ignition switched power. If the fuse only blows with the engine running, perhaps there is a short in a circuit supplied only with power from the stator such as the automatic enricher or headlights on many scoots. If your scooter has a fuse box with multiple fused circuits and only one fuse blows, thoroughly examine that circuit.
Try to have a wiring diagram handy to help you identify wires and circuits. With most Chinese scooters the best you're likely to find is a somewhat generic diagram from a similar scooter. There are some diagrams HERE
. If you can find a service manual or even an owner's manual for your scooter it may have a wiring diagram. Find some manuals HERE
There are a few ways to try and track down a short. One of the easiest to perform is a visual inspection. On most scooters this will require removing body panels. Trace the wiring and look for any obvious signs of a problem. These include bare sections of wires or connections, a wire or harness being pinched against the frame or other metal components, a screw penetrating a wire, or burned or melted wires or connectors.
A multimeter (DMM/DVOM) able to check resistance / ohms (Ω) could also be used. Many auto parts, department, and home improvement stores sell them. You can usually find one very cheap at Harbor Freight, or sometimes they give them away free with a purchase if you have a coupon. To use a multimeter to find a short :
- Disconnect the battery. Secure any cables removed so they do not touch any source of power or ground or battery terminals.
- Set the multimeter to it's ohm / Ω setting. If your meter has many ranges, select the lowest, which is often marked as 200.
- Connect the black probe from the multimeter securely to a source of ground such as the negative battery cable or bare metal on the frame or engine. Touching the other probe to another ground should give you something very near 0Ω of resistance and verify that you have chosen a good location. You may not see exactly 0Ω because many meters display some fraction on an ohm even if both probes are touched together so it reads as low as possible.
- Connect the multimeter's red probe to any positive wire you wish to test. Usually you would want to start by connecting the probe to the side of the fuse holder's wiring that goes into the harness or toward the accessory, not the side that goes to the battery or power source.
- Check the multimeter's display.
-If it reads infinite resistance, often displayed as 0.L on a digital multimeter, then there are no shorts to ground present in that circuit under the current conditions or you aren't making good contact with the probes.
-If it displays 0Ω, or very near 0Ω, then there is a short to ground somewhere within the circuit.
-You may see a reading that's not near 0Ω, but also not 0.L. It is normal for components connected to the circuit to cause readings that are below the top of the meter's scale so it cannot display 0.L, but this does not mean there is a problem with a short circuit. A short should be very near 0Ω because current can take a direct path.
You can also use specialty testers designed for finding shorts. These can be much more expensive than some multimeters, and they may not include the functionality for other types of test that a multimeter has. Their big benefit is that some can make finding shorts or other wiring problems easier. Most use lights or tones to indicate a short, and some will even tell you which direction the short is in or flash or beep with greater intensity when near a short. A search should bring of plenty of these devices and instructions for their use.
Some advise the use of a test light to check for shorts. What most say is to disconnect one of the battery cables. The test light would then be installed between the battery terminal and the wire that you disconnected from the terminal. Another option is to leave the battery hooked up, but to put the test light in place of the fuse that is blowing. Then it is said that if the test light illuminates, there is a short somewhere in the circuit. It sounds like a very easy method of finding shorts, until you actually try it. If the test light does not light up at all, you can be sure there is not a short nor any significant conductive path from power to ground within that circuit. For that, it succeeds.
The problem comes when there is anything else in the circuit that would act as a conductive path, such as a light bulb or various other components common on scooters. Most test lights require very little current to illuminate, so even normal components that are not malfunctioning may cause the light to come on. This is the same reason that I mentioned earlier that you are likely to get resistance readings that are not 0Ω or infinite when using a multimeter. The difference is that the multimeter will allow you to see exactly what the reading is, while a standard test light only shows a connection or no connection. Some will be more dim when there's a very weak connection, but it's still at least much harder to tell a short from something ordinary that's not an issue without unhooking everything on the circuit.
A test light or makeshift test light that requires more current to fully illuminate would work better. Some troubleshooters use a sealed beam headlight as a test light. You may even be able to use your scooter's headlight in the housing (to protect the bulb and protect yourself from burns). The idea is to make a connector to a power terminal on the headlight and one to ground on the headlight. Each with long wires and perhaps clips on their ends. Then the headlight could be used as a sort of high current test light. Minor conductive paths should only allow the bulb to be very dimly lit. A major conductive path, such as a short to ground, should need to be present for the headlight to reach full brightness. I feel a multimeter is much easier to use and serves many more purposes, and when their potentially low cost is considered it's a hard tool to beat for this and other scooter related jobs.
Regardless of the tool used to locate a short, once you've found evidence of one you need to narrow your search until you know exactly what the problem is so it can be corrected. This will likely involve disconnecting components until the short goes away. If you end up with all components of the wiring harness disconnected and still find continuity between power and ground then you will need to do a close inspection of wire harness by removing any covering and tracing wires to look for damage, wear, etc...
Intermittent shorts can be very tricky, since they aren't always present. If you have trouble locating a short you may find that wiggling a connector or wire harness allows the short to occur. Usually this is because of damaged wiring that is not always making contact with a ground. Wiring problems can be very frustrating, so if you find yourself growing aggravated it's best to walk away and come back to it later.
I have provided an example of a short finding process below in case it's of any help :
Related Info :
More Wiring Diagrams
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- The scooter's main fuse blows whenever the horn button is used.
- Using a multimeter shows 125Ω between the fuse holder's wiring harness side and ground when the key is on, engine off. This is presumed to be normal resistance from other components in the system.
- When the horn button is pressed, resistance changes from 125Ω to 0Ω. When released resistance goes back to 125Ω. This tells us that there is a short to ground somewhere within the horn circuit, which includes a horn button in the left hand control assembly, a horn, and wiring between them.
- Nothing changes with the horn disconnected. This tells us that the horn should not be the source of the short and narrows our search to the horn button and the wiring between the horn and the button.
- The horn button is disconnected from the wiring that connected it to the horn and resistance still jumps from 125Ω to 0Ω when the horn button is pressed. This tells us that the issue is within the horn button.
- The left hand controls containing the horn button are removed. It is found that the wire leading from the horn button toward the connector to the horn has a bare spot that is grounding against the metal hand control assembly to create a short. The wire would then need to be repaired or replaced, or the whole assembly could be replaced, to correct the problem.
- To be totally thorough, the wires between the horn button and horn are checked while disconnected to verify that there is no other problem in the circuit. No continuity is found, so fixing the horn button should solve our problem.