Basic Electronic Troubleshooting

Ahhh the motorcycle's electrical system

The wiring diagrams look like a complex alien map but with a little understanding of the basics you can start to tackle it.
The wiring diagrams look like a complex alien map but with a little understanding of the basics you can start to tackle it.Photography by Mark Zimmerman

If there’s one thing that confounds the average do-it-yourselfer, and quite a few professionals for that matter, it’s a motorcycle’s electrical system. That’s perfectly understandable; unlike a mechanical device, where the action is often easy to visualize, electrical activity occurs at a subatomic level. So unless you’ve got really good eyes, it’s hard to picture what’s happening. Fortunately, while electrical theory may be complex, basic electrical work, including troubleshooting, repairs and adding accessories are much less so. While the following may seem elementary to the electrically proficient, it should point those of you that don’t know their amps from a hole in the ground in the right direction.

Good Things Come in Threes
Before we delve into trouble shooting, let's review basic electrical theory. As you may recall from your school days, an electrical system can only function when three things are present. First, we need a power source; in this case, it's the motorcycle's battery, and for convenience, we'll lump the source in with any necessary wiring and switches. Second, is some sort of electrical load, for example a starter motor or light bulb, and last is a pathway to ground. If all three are there, we have a "complete circuit," and our electrons can accomplish something useful.

Once you understand that, troubleshooting becomes relatively easy. If one of those three components is damaged or missing, then our circuit is incomplete (or open), and can’t function.

By no means am I suggesting that all electrical troubles are quick or easy to solve. Intermittent problems like a charging system that randomly cuts in and out, or a voltage drop issue wherein a component (say, a starter motor) receives enough voltage to work, but not enough to work well, can be excruciatingly difficult to pinpoint, even for an experienced tech, but a good percentage of electrical problems the average rider encounters are caused by something straightforward like a broken wire, bad ground or a failed component.

The lighting circuit diagram shows you the complete "three-part" system.
The lighting circuit diagram shows you the complete "three-part" system.Courtesy of Triumph

My first suggestion—and this should be done before there's even a hint of trouble—is to familiarize yourself with your motorcycle's electrical system. You should know, for instance, where the fuses are located, which circuits are individually fused, and what type of fuses the bike uses. You should also glance through the wiring diagram, especially if you've never used one before. Initially, it'll look like hieroglyphics, but stick with it until you have at least a basic understanding of how the circuits are arranged and what each one controls.

Be forewarned though; interpreting a wiring diagram is an acquired skill, and some are a little tough to follow, especially since the OEM’s all have their own formats. Furthermore, the symbols used to represent the assorted components might best be described as non-uniform, especially when you’re perusing an Asian manual.

The European bikes are a little better in this regard, since most subscribe to the DIN/ISO format, which standardizes terminal designation and wire color-coding. Under the DIN system, for example, terminal #15 is always the output side of the ignition switch and it’s always connected by a green wire to terminal #15a on the ignition coil. It’s an easy-to-understand system, and if I had my say, would be adopted by the rest of the world’s motorcycle manufacturers.

Be familiar with the tools before a problem occurs.
Be familiar with the tools before a problem occurs.Photography by Mark Zimmerman

Besides learning to use a wiring diagram, you should also familiarize yourself with two basic test tools: a test light, and a DVOM or Digital Volt Ohm meter.

Of all the electrical troubleshooting tools available, nothing is as easy to use or as versatile as a plain old five-dollar test light. The test light (which is nothing more than a light bulb connected to a probe at one end and an alligator clip at the other) can only tell you if voltage and a ground are present, but trust me, that’s handy information to have when you’re trying figure how why something stopped working.

On the downside, the test light can’t be used to measure anything. So if the problem involves something like high resistance or low voltage, you’ll need a more sophisticated instrument. For an initial assessment of the problem, however, a test light is worth its weight in gold. Test lights can be found just about anywhere tools are sold and retail for somewhere between 5 and 50 bucks depending on whose name is on the box.

The DVOM (Digital Volt Ohm meter), is the electrical repairman’s jack of all trades, and once you learn how to use one, there won’t be many electrical problems you can’t solve. A DVOM lets you measure things like AC and DC voltages, resistance, amperage, continuity, and so on. Some of the high-end models even have the ability to measure temperature and noise levels. I should mention that while you may occasionally stumble across the older analog-style meters, using them on newer motorcycles isn’t a particularly good idea; analog meters tend to have high internal resistances, so they can be less than accurate, and I’ve also heard of them damaging sensitive computer-driven components (plus they’re hard to read). Good DVOMs start at about $20.00 at Sears or radio Shack, but really good ones, like the Fluke 88V ($419.95) go for considerably more. Buy the $20.00 version and get to know it.

A test light can be a great sidekick when troubleshooting your electrical problems.
A test light can be a great sidekick when troubleshooting your electrical problems.Photography by Mark Zimmerman

The Process
All electrical troubleshooting needs to be performed as logically and systematically as possible—a task that's often easier said than done, especially if you're on the side of some dark and lonely road. Rather than go off half-cocked and start pulling wires apart, stop; catch your breath and take it step by step, and remember that logic is your friend. First off, what circuits or sub-circuits are affected? Is it one or two, and are they related? If nothing else, once you've got that figured out, at least you've got a starting point. For example, if you lose all the lights, including the turn signals, it may be that the light switch has simply come unplugged, or in some cases where circuits share a common fuse, that the fuse has blown. However, if you lose only the right-side turn signals, you can reasonably assume that, while the switch itself or some portion of the wiring may be at fault (and I stress 'may') the light circuit as a whole is intact and you can confine your search to the turn signal circuit. Obviously, this is where your wiring diagram earns its keep, but you already knew that, right?

Think the problem through: did it start after some accessory or wiring modification was performed? Does the problem occur when the bike sits or after a period of heavy electrical use or under specific circumstances (like when you’re wearing a heated riding suit)?

The mantra here is to be deliberate and use your shop manual; many contain step-by-step troubleshooting guides that will lead you more directly to the problem.

Let’s look at two simple electrical failure scenarios.

The DVOM (Digital Volt Ohm Meter) is the electrical repairman's jack of all trades.
The DVOM (Digital Volt Ohm Meter) is the electrical repairman's jack of all trades.Photography by Mark Zimmerman

Scenario 1—Rear Signal Light Failure.
During your weekly walk-around inspection, you notice the right rear signal light is out. You do the logical thing and replace the bulb, which fails to light. So now what?

Connect the test light ground to a solid frame ground (the negative post of the battery being the best one), then energize the signal and touch the test light probe to the bulb’s terminal. If the light doesn’t come on, voltage isn’t reaching the terminal.

Identify the wire that carries voltage to the turn signal. Since you’re new to this, use the wiring diagram to avoid mistakes. Then work backwards from the turn signal light, testing the circuit until the light comes on, indicating voltage. Your first inclination may be to poke holes in the wire’s insulation and test it every few inches, which generally isn’t the best plan, partly because it compromises the insulation, and partly because wires rarely break in the middle of their lengths. Typically, the problem will be found where a connector is crimped on to the wire, where two, multi-pin “cannon connectors” plug together, or where the wire takes a sharp bend or rubs on a rough edge. To make the job easier, look for large connectors where you can separate the harness, and test there first. This will help narrow the search. Be sure to probe both sides of any multi-pin connectors you find. Very often a wire will test fine where it enters the connector, and be as dead as a doornail where it exits. When that happens, look for a wire that’s broken off its pin, or a bad connection, perhaps caused by corrosion or physical damage between the male and female connectors.

If the light came on (indicating voltage), you’ve got either a bad bulb or a bad ground. To determine which, locate the light’s ground, connect the appropriate side of your light to it, then touch the test light probe to the energized signal terminal or to the battery’s positive post. If the light doesn’t come on you’ve got a bad ground; if it does, the new bulb is bad (rare, but it does happen). I should also mention that it’s a wise man that checks his test light before each use— you’re going to feel really silly if you spend an hour testing a circuit only to discover you’ve got a bad test light bulb.

Scenario 2—Bad Battery (Or is it just misunderstood?)
After not riding the bike for several weeks, you try to start it. The engine cranks slowly and fails to start, and after a few tries it gives up the ghost. Is the battery dead or are there other problems? Here's where the DVOM meter pays for itself.

With the meter set on DC voltage, touch the probes to the battery’s terminals. If the meter shows something less than 12.5V we’ve got low battery voltage, and your chances of getting the bike started are slim. For our purposes, we’ll assume the reading is substantially below that. The first step is to charge the battery and retest it; a fully charged conventional battery should read between 12.6 and 13.8 volts (the higher the better). We’ll assume here that the battery took a charge and your meter reads 13.5 volts.

The question now is why did the battery go dead? Reinstall the battery and connect the voltmeter, noting the no-load voltage. Turn on the key, and while watching the voltmeter, hit the starter button. As the engine cranks the voltmeter reading should remain at something above 9.5 volts (at 70 degrees Fahrenheit).

As a rough guide, figure a carburetor-equipped bike requires around 200 to 250 watts to keep itself going, while an EFI bike may need anywhere from 250 to 350.

If it falls to 9.5 or less, the battery is on its way out and will need replacement. If it remains above 10 volts, it’s good. Once the bike starts, watch the reading at a fast idle: the voltage should read close to 14 to 14.5 volts. If the reading stays at the no-load voltage or below, the charging system is on the fritz. If everything looks good on the meter, you need to ride more often, or leave the bike on a charger between rides. By the same token, if this situation occurs on a bike that’s ridden often, you’ll have to delve a little deeper to find out what’s killing the battery when the bike is parked. Granted, the above examples are relatively simple problems, intended primarily to illustrate how DVOMs and test lights, along with the shop manual and a little logic, can track down an electrical fault. More involved problems, for example, those dealing with voltage drops, high circuit resistances, or parasitic draws, will require commensurate effort to solve. My suggestion, should you have any real interest in that direction, would be to read through the appropriate manuals on the subject. I’ve listed some of my favorites in the sources section.

Adding Accessories
Back in the day, a louder horn or a pair of spotlights was the last word in electrical accessories—and I mean the last word in a literal sense. Adding too many gadgets often overloaded the charging system's meager output, especially when the bikes were ridden in stop-and-go situations or at low speeds, so in most cases electrical add-ons were kept to a minimum, or at least used judiciously.

Modern bikes are much better in this regard. Not only are the electrical systems more reliable, but they’re also capable of handling much larger loads. This doesn’t mean they can’t be overloaded—only that it takes more effort to do so.

Subtract what it takes to run your bike from the alternator's output, and whatever's left is what you'll have for the fun stuff like iPods, heated suits and microwave ovens.

Fortunately, there’s an easy way to avoid trouble. All electrical devices carry a wattage rating, watts being an indication of how much power an electrical device produces or consumes. So long as our charging system produces more watts then the electrical system uses, everything is Jake.

Normally, specifications for alternator output, as well as the wattage of common components like the running lights and headlamp, can be found in the shop or owner’s manual. However, figures for the ignition and EFI systems generally aren’t provided, which can make pinning down an exact number sketchy.As a rough guide, figure a carburetor-equipped bike requires around 200 to 250 watts to keep itself going, while an EFI bike may need anywhere from 250 to 350.

Subtract what it takes to run your bike from the alternator’s output, and whatever’s left is what you’ll have for the fun stuff like iPods, heated suits and microwave ovens.

For example, the 2001 Vulcan 1500 fuel-injected) charging system pumps out 588 watts, which is pretty healthy for a cruiser. Of that, it uses 340 watts to propel itself down the road, which leaves 248 watts for toys.

Of course you’ll still need to know what your electrical accessories draw. Here’s what a few of the more popular items use: Cell phones, radar detectors and most portable music systems require between 1-3 watts to run, a GPS maybe 6, a typical laptop around 50 watts, and heated riding gear, 100 to 250 depending on how much you’re wearing and how high you’ve got it turned up. Auxiliary lights can draw from 30 to about 100 watts apiece.

Bottom line, if you’re touring on your Vulcan with every stitch of electric gear you own maxed out, you’re crowding the capabilities of the charging system. Switch on those driving lights, and you may find that the bike won’t start after the next pie and coffee break. Installing a voltmeter or charging system monitor so you can keep tabs on the system is a good way to avoid problems, and much easier than bump-starting a bike when you’re full of fresh pie and coffee.

While electrical theory may be complex, basic electrical work, including troubleshooting, repairs and adding accessories are much less so.
While electrical theory may be complex, basic electrical work, including troubleshooting, repairs and adding accessories are much less so.Photography by Mark Zimmerman

In Sum
Electrical work isn't always intuitive, but it's not black magic either. Since the forgoing was as basic as it gets, I'd recommend the following books to help fill in the gaps.

Reading List:
Motorcycle Electrical Systems—Trouble Shooting and Repair
Tracy Martin
MBI Publishing
An excellent guide to the practical side of motorcycle electrical repair. If you've got this, a shop manual and a few basic tools, you'll be able to fix just about any electrical problem you run into.

Motorcycle Electrical Manual—A Comprehensive Guide
Tony Trantner
Haynes Publishing
This one is heavy on theory and not so much hands-on. My volume is over 30 years old though, so the latest version may be a little different in that regard.

Change is good when it comes to antifreeze.
Change is good when it comes to antifreeze.Cruiser

Change is Good

Tech Tip
When's the last time you changed your bike's antifreeze? Can't recall? Don't be embarrassed, neither can I, and that's probably true for far too many of us.

In techno-speak, antifreeze is a cyroprotectant, meaning that its substance is used to prevent the formation of ice crystals in something that would be better off unfrozen. In its primary role, antifreeze prevents the water in your bike’s cooling system from turning into a rigid and highly destructive internal engine component whenever the temperature drops below freezing. Antifreeze also raises the boiling point of water (in this role it’s referred to as a colligative agent) so it provides a degree of protection against overheating as well.

Typically, antifreezes are created from a family of alcohols called glycols. Ethylene glycol is popular for use in things like internal combustion engines and solar heating systems, while its near-relative, propylene glycol, is sometimes used to prevent ice crystals from forming in ice cream. As you may imagine, confusing the two would have unpleasant repercussions, but at least the ice cream wouldn’t overheat.

Because motorcycle engines use lots of easily corrosible materials, aluminum being one of the worst, antifreezes contain corrosion inhibitors— silicates, phosphates and borates being the most popular, to keep it alkaline. Unfortunately, the inhibitors don’t last forever and as they’re depleted, the antifreeze becomes acidic. Once that happens, internal corrosion starts to become an issue, which is why the OEMs recommend changing coolant regularly.

There is a caveat though. many auto parts stores, particularly the ones that do a lot of heavy truck business, carry coolant test strips. In reality, these are nothing more than a piece of litmus paper that can be used to check the Ph of your coolant. If the coolant falls into the green zone, there’s no need to replace it. If it doesn’t, change is in the air.

Your shop or owner’s manual should provide the 411, but essentially, it goes like this:

Locate the cooling system’s drain bolt, which should be located at the system’s lowest point.

Loosen the radiator cap, and remove the drain bolt. In many cases you’ll also have to remove the reserve or expansion tank’s siphon hose.

Drain the old antifreeze into a sealable container. Antifreeze is highly toxic, and it only takes a few ounces to kill a healthy adult. It has a very sweet taste, which makes it attractive to children and animals. I can’t stress how dangerous this stuff is, so dispose of it quickly and properly, especially if you’ve got kids and pets, and promptly hose down any spills to dilute it.

If the system shows signs of corrosion, flush it using cool water. If it’s really bad, you may need to remove the radiator and have it professionally cleaned.

Refill the system with fresh coolant. If you’re using straight antifreeze, a 50-50 mix of antifreeze-to-water will protect your engine to -34 degrees Fahrenheit and prevent boilover to 265 degrees Farhenheit. And yes, if possible, mix the stuff with distilled water. Personally, I find the pre-mixed stuff to be more convenient, but either type works fine. Oh yeah, if you’re buying the antifreeze from a discount or auto supply shop, make sure it’s approved for use in an aluminum block/head engine. These days it all should be, but who knows?

Once the fresh stuff is in, warm the engine up, and following the manual’s instructions, bleed the air out of the system. Then top off the system.