To do a competent job restoring an old motorcycle, you need basic electrical knowledge. You probably know much more than you realize.
Electrical systems are no more difficult than working on carbs or brakes, but unlike those things, there are very few good basic guides to electrical systems for beginners. Hopefully reading this section will help you.
I’ll discuss electrical systems, using similar systems that are also important to our work, to help you understand. You’ll see hydraulic systems (like disc brakes use) and pneumatic systems (like air systems and tools in a shop) are very closely related to electrical systems.
I’ll use & describe North American terms of measurement in the examples. So folks in other countries, you may need to relate Pounds per Square Inch to Kilo Pascals, electrical ground is what you’d call Earth and so on.
A very simple electrical example would be a battery, some wire and a light bulb. Most folks could easily connect the parts and make the bulb light up. You already know that the battery holds a store of electrical power, the wire is used to transport that power and the bulb uses the power in order to produce light. You also know that if the light is left ON and there’s no way to recharge the battery, eventually the battery will die.
You also know that if one of the wires is disconnected, you no longer have a full “circuit” – and a circuit is required so electrons flow from the battery, through the wires to the light and back to the battery. A circuit that is broken is called an “open”. This is a real-life electrical problem that can occur. An “open” circuit is sort of one extreme, with next item being at the other extreme.
If a wire connected to one terminal on the battery was to accidentally contact the other terminal, you’d have a “short” – meaning the power is routed directly from one side of the battery. This may cause sparks, and even on small scale systems will cause heat, a potential fire risk, and seriously damage your battery. Of course, if a circuit is broken and a wire carry power is dangling around, initially you have an open – but if that wire contacts some other metal object, a short circuit may occur.
OK so far ? – This sums up just about everything most folks would say they know about electrical systems. So far we’ve only looked at two issues at extremes – open and short circuits. But the worse problems of all are fall somewhere in between. Let’s relate what we know to other types of systems and as we do, we’ll delve down into more detail.
A simple air system equivalent would be a tank of compressed air, some air hoses and a paint gun. The tank of compressed air is much like a battery – that compressed air is a store of “potential” work that can be done. A hydraulic system is very similar – a tank containing pressurized fluid, some hoses and some form of tool that will do work when hydraulic fluid under pressure is routed to that tool. That’s hardly Earth shattering knowledge, right?
In electrical systems, a battery is a store of potential work. Small batteries are measure mainly by their rated volts. In air and hydraulic systems with storage tanks, we talk about pressure in terms of “pounds per square inch” or PSI, the pressure in the tank. But there’s more to this, and again, you will probably realize that you know a lot of this to some extent.
Imagine we tried to start a big diesel pickup truck with 12 volt electrical systems, using only a small 12 volt battery from a motorcycle. Even if that battery is brand new and at full charge, the truck’s starter won’t do a thing. We need a bigger battery – that much you probably realized at the outset! But why do we need a bigger battery? We don’t need more volts – we need more amps, often referred to as “cold cranking amps” if you read automotive literature. If that’s confusing, don’t panic, read the next example.
If you have a small shop air compressor that tops out at 150 PSI, do you think it would power a full sized jackhammer? No. You would need a much greater volume of air – even though in theory you have enough pressure (PSI). So, “cubic feet per minute” or CFM, the ability to deliver enough volume at the working pressure is the vital measurement.
PSI and CFM work together just as Volts and Amps work together!
For the purposes of the above example, we could simply substitute the wording “hydraulic system” for “air system” and the same considerations still apply. Each type of system requires a form of energy (volts or pressurized air or fluid) and some capability do deliver “flow” of that energy for a certain period of time without either the energy or flow rate dropping off too much. So you see, the theory behind each of these systems are very closely related.
It is a shame in a way that we don’t use the same terminology for each power system – if you understand one system, it’s not like learning a new language to learn the other systems!
There are also considerations specific to each type of system, but even those “system specific considerations” can be related to the considerations for other systems. Let’s say you have an air system in your workshop and it WAS working fine. Now you notice that your air tool is working slow and you maybe can hear air rushing somewhere. You check the lines and find a leak. We already know that air systems need pressure and volume in sufficient quantity to do useful work. So fix the leak. This example would directly apply also to hydraulics. But what about electrical?
Electrical systems can have “leaks” too but they’re not always easy to spot. A leak in an pneumatic or hydraulic system is usually pretty obvious, making a lot of noise or mess, as well as the reduced capability to do work. But unless your electrical system is sparking somewhere, the problem may be elusive. Let’s say you have a motorcycle headlight system that was working fine even with the motor off just “key on” and running from the battery, but now the lights are dim or they don’t even work, though the battery is at full charge. A leak in electrical is called “voltage drop” or “voltage leak” which is similar to a loss of pressure in a pneumatic or hydraulic system. We have to be systematic and pay attention to detail to find voltage leaks, much as we must be very careful diagnosing problems with carbs or brakes.
Mobile Electrical Systems – Let’s stop and think about mobile electrical systems, as used in motorcycles, cars/trucks, boats and even aircraft. Mobile systems present a couple of issues that designers try to cover.
Vibration – Unlike house wiring with solid core wire, we use multi-strand wire and the wiring must be secured well. To avoid vibration causing wires to chafe against a chassis, we can use shielding and use care in routing wiring and control cables to mitigate this risk.
Waterproofing – Dealing with environmental extremes is also typical of mobile systems so water proofing is critical.
Common Ground – There is also an issue that can be turned into opportunity in mobile systems – often we have a vehicle chassis made of metal. Frequently the metal chassis is used as a “common ground”. So long as we send power from the battery to a light switch and on to a light or horn, we will have a complete circuit IF the battery’s ground is connected to the chassis and that light or horn is also electrically grounded to the chassis.
Common ground systems use the chassis as a convenient ground connection for many circuits. But remember, the success of the common ground system relies on a good connection between battery and the chassis. And just to muddy the water a bit, note that many mobile systems using “common ground” may still require ground wires from fixtures to ground to the chassis. It’s not always as simple as ensuring that the fixture is securely mounted.
Every electrical connection, no matter what type, must be clean, electrically “bonded” to the next electrical part in the circuit and protected from the elements.
No Tools Required, Yet – We don’t always need specialized tools to find electrical problems like voltage leaks, even though they are not as obvious as a puddle of hydraulic fluid on the floor or a roar of air blasting from a hose.
Here is a fundamental test you should always remember. A very simple test for voltage leaks is to remove one cable from your battery while the bike is entirely shut off. It doesn’t matter which cable you use. Now just brush the cable against it’s terminal on the battery. Watch and listen carefully. If you see a spark or hear a little crackle sound, then the battery is being subjected to current flow demand even though everything appears to be shut off.
Leaks can result from a poorly maintained system. Often a bit of condensation at an electrical connection is not enough to cause a full-on short circuit but enough to divert some power to ground. This is very common with old bikes.
The best solution to eliminate these problems on a motorcycle you’re restoring, is to methodically inspect and clean every connection on the bike. It takes a few days of casual work – the benefit is clear – reliability. This may not trap all the gremlins but at least if you do a thorough clean-up of the electrical connections, subsequent trouble shooting is much easier when you are sure that the basic connections are clean, dry and properly connected.
Sometimes you will find that a previous owner has wired in an aftermarket item like a stereo that constantly draws a bit of power even when the bike is shut off, so you don’t have to reset the time display etc.
What The Heck?? OK, you’re perhaps bored and want to know “What the Heck is wrong with my bike? It does this or doesn’t do that…” You need to be methodical. The electrical systems on a bike involve charging, ignition and electrical accessories like lights, horn, etc. So don’t panic, think objectively, try to define which area is truly involved. Before we go further, here’s an important point.
It’s Working, Now It’s Dead! – Almost unique to electrical systems that you should bear in mind. Components of electrical systems, more so than any other system, often do not have the good graces to up and die. Even a ground connection from battery to the chassis, that is intermittently “good” and then “open”, can drive you nuts unless you’re methodical about checking everything. “Where to start?” – we’ll work on that as we continue.
For example, like charging system rotors and stators, ignition system coils, etc., may all work and even test fine, especially when cold and then abruptly fail when you’re miles from home. The reason for this is simple, a fault may not occur until an component heats up and expands, causing a crack to open and an “open” circuit situation to occur. In the situation of charging systems components, some simple multimeter tests are the best course for diagnosis. I’ll cover them in detail in a specific topic discussion.
The SINGLE MOST IMPORTANT TEST FOR ELECTRICAL FAILURES on common ground systems is bad grounds. No sweat, we have a very simple testing process for that.
If we’re talking about ignition coils on a multi-cylinder bike, the motor may still run but with obviously less power. You should first check for spark at each cylinder. Don’t fuss with pulling plugs, just take a spare with you, put it in #1 plug lead, crank the bike and see if you get spark, then do the next. If you identify a cylinder with no spark, try swapping it’s coil and plug lead with another cylinder. You can even try swapping a plug lead first to see “is it the plug lead?” and then if no joy, swap coils.
This topic is under construction, check back soon for more detail and links to sub topics.
Motorcycle Electrical Troubleshooting
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