Motorcycle electrical systems have been known to strike fear even into some of the most seasoned home motorcycle mechanics. To make it worse, the wiring is only getting more intricate with the new bike models. Electrical problems often cause an instant phone call to schedule an appointment at the bike shop. But it doesn't have to be that way. Troubleshooting electrical problems is simply understanding what each component's function is and then troubleshooting to eliminate them as the source of the problem. Knowing where to start is the biggest hurdle.
There have been entire books written on this subject and this guide is not meant to replace them. It will, however, help riders understand what each electrical component's function is and what problems they can cause if they are malfunctioning. The purpose of this guide is to help riders to begin the process of troubleshooting motorcycle electrical problems.
You will need a multimeter and the shop manual for your specific motorcycle to troubleshoot the electrical system.
Before you go through the process of technical troubleshooting, you should go back and eliminate the possible "whoops, forgot about those" issues. It's happened to even the most knowledgeable mechanics. Check the kill switch/button and the key. Your bike may also have safety cut outs that will prevent you from starting the engine. Some bikes will not start with the side stand down, if the bike is in gear or if the clutch lever is not pulled in. Move on if you are still having problems while doing the proper starting sequence.
A great place to start is at the source of power. You need to make sure that your battery is in working condition. (If your bike does not have a battery, you can move on to the next steps.) First, check to make sure that the battery has a full charge. The battery should have 12 volts or higher with no load on it (ignition and lights off). If the battery only measures to a maximum of 10.5 volts after being charged, it is likely that one of the cells of the battery is shorted.
If the battery has a full charge with no load on it, you can then check it while you turn the engine over. A battery may fully charge, but then drop significantly when under load. If the battery drops below 10.8 volts, it is possible that the battery is no longer operable. Significant engine trouble can also cause the voltage to drop too far if it is making it difficult for the starter to turn the engine over. A good way to tell if this is happening is to check the battery cables for excessive heat. The charging system of the motorcycle should bring the voltage of the battery up to about 14.2 to 14.8 volts. Anything over that and the system is overcharging. Anything under and the charging system is not able to keep up. In both cases, something in the charging system needs to be fixed.
It's possible for your motorcycle to start and run with a bad battery, but that can create even more problems like causing the bike to run poorly and miss. It's also important to make sure that the battery that you use produces enough amps to properly power all of the electrical components.
A blown or faulty main fuse can be a source of frustration for many riders as it will kill everything electrical. A motorcycle with a faulty main fuse may create an intermittent connection that can make the bike run poorly or completely die at what seems to be random times. This can be frustrating if not diagnosed right away as it will make it seem like there is something else wrong with your bike. A main fuse can become faulty due to age or excessive vibration. It's a good idea to keep a spare main fuse on hand at all times because they can go at any time. If the fuse continues to blow, you will have to check other components of your electrical system to see what is causing the excessive amperage.
Faulty wire grounds are a very common problem, but can sometimes be difficult to track down. Symptoms of a bad ground can range from a completely dead bike to electrical components working intermittently. Checking all of the grounds on your motorcycle can be done quickly if you know where they all are. If you don't, your service manual should have all of the locations noted.
Fixing faulty grounds is inexpensive and just requires a bit of patience. It's a good idea to check for faulty grounds early in the troubleshooting process.
If you are having problems with charging, you should first check your stator since its job is to provide the extra power needed to charge the battery during operation. If the stator doesn't provide enough power, the battery will begin to drain. For troubleshooting, the stator connector that runs to the engine m ust be unplugged. With the connector unplugged, you can test the stator for both resistance and voltage.
To begin, you should first check for continuity from the terminal tabs of the connector and then see if anything goes to the ground. Set your multimeter to Ohms to check this. First, use the multimeter leads to check the resistance of the tabs by checking A to B, B to C and then A to C. The multimeter should read under 1 Ohm for all three (make sure to take into account the resistance between the leads). Readings over 1.5 Ohms are an indication that the stator is faulty.
Next, check to make sure nothing is going to ground by connecting the red lead to the connector and the black lead to the negative terminal of the battery. This should be an open circuit and the meter should not read anything. If it does, the stator is faulty.
Now, switch your multimeter to read AC voltage. To check for voltage, the motorcycle must be running and should be at about 2000 rpm. Then, measure the voltage from tab to tab, just like before. The actual number of the voltage is not terribly important. What you are looking for is that all three of the numbers are similar. If the voltage numbers are more than a few apart, the stator is faulty.
The regulator/rectifier on your motorcycle performs two functions. The rectifier portion converts the AC power from the alternator into DC power so that it can charge the battery. The regulator ensures that the voltage is delivered within certain limits, as not to damage the battery. Excess power is converted into heat by the regulator to get rid of it. The regulator and rectifier are often together in one unit, but for some bikes (mostly older), they can be separate.
To test the rectifier, you will need to disconnect all of the wires and turn your multimeter to the diode function. First, check the positive diode. To do this, place the positive lead into the positive diode. Then connect the negative lead to each of the stator inputs. The meter should not read anything on any of these. If that checks out, connect the negative lead to the positive diode and connect the positive lead to each of the stator inputs. The meter should now be reading something. The numbers are not important.
Repeat the process for the negative diode. This time you should get a reading with the positive lead connected to the negative diode while connecting the negative lead to the stator inputs. With the negative lead connected to the negative diode, the meter should not read anything while connecting the positive lead to the stator inputs.
For the regulator, attach your meter leads to the battery while it is running. It should not read higher than 14.5 volts and no lower than 13.5 volts. If it is higher, the battery will be over charged and if it is lower, the battery will continue to drain as the bike runs.
If these tests do not check out, you will need a new regulator/rectifier.
If you are having a no-spark problem, a good place to start after ruling out shorts, grounds, switches and spark plugs, is the ignition coil, spark plug caps and wires. The plug wire runs from the ignition coil to the plug cap. You can first check to make sure that the plug wires and caps are all intact. A breakdown in the insulation can cause arcing in the plug wire. You will be able to see the wire spark in low light conditions. Plug caps may be cracked, which can cause corrosion or an open circuit. To test the cap, you will need to remove it. Use your multimeter to check for resistance. It should read in the thousands for Ohms.
If your plug wires and caps check out, you can now test your ignition coil. First measure the resistance between the primary wire that comes from the CDI box and the ground or ground wire. The resistance should measure around .5 to 1.5 Ohms. If that checks out, you can then measure the resistance between the secondary wire (plug wire), w hich should measure in the thousands. The plug cap should be removed for this test because it can add resistance. Your shop manual should have the correct specifications for your specific ignition coil.
Pickup coils rarely go bad, but at times they do. Fortunately, they are not that difficult to test. To begin, you will need to unplug the connector. Connect your multimeter leads to the connector and check for resistance by setting your meter to Ohms. Compare your readings with your shop manual's specifications to see if they are within range. You can also check the gap between the coil and the magnet. Make sure that it is gapped to the manual's specs.
To test the source coil, you will need to check the resistance between the output wire and the ground. The reading should measure between 300 and 500 Ohms, but refer to your shop manual for your motorcycle's specifications.
Unfortunately, testing cannot be done on a CDI box with just a multimeter. The only way for a home mechanic to test for the CDI is to swap it with a CDI that is known to work. It's for this reason that the CDI should be the last thing that you check. They can be expensive and if it was not the problem, you can be stuck with two working CDI boxes. Eliminate everything else before you buy a new CDI, unless you are fortunate enough to have access to another working box.
Note- If your motorcycle starts and runs fine, but then dies once it warms up, there could be a wire somewhere in the ignition circuit that is losing connectivity as it warms. If this is the case, you may have to purchase or have a shop test your coils with a load tester. You might also be able to simulate the heat by using a heat gun to warm the coils. You can then test the coils as they are being warmed up.