Basic Electronics for Bikers
Volts, amperage (current), resistance, continuity, Ohms, Watts - sheez, a whole new language and the concept of a new language is what throws people. So lets break it down to something easy to understand. You still have to learn the terms though, cause that's what everyone uses.
Volts - With one exception (the stator and we'll get to that later) we use 12 volts DC in our bikes. Think of volts as the available energy to do something. Kind of like muscle tone in your body.
Resistance - measured in Ohms, and just like it says it resists the force you place on it. As you put a bolt in a nut, the bolt turns real easy until it begins to tighten, then it meets the resistance of the metal nut. The more resistance the nut places on the bolt threads, the more muscle you have to use.
Amperage (current) - measured in Amps or some portion of an amp (milliamp, microamp, etc) this is what does the work. How much muscle you use to tighten the bolt in other words.
If you think about what I just said, it should seem obvious that you must have all three things to get anything done. You have to have some available muscle (voltage) to turn the bolt and how much muscle is used (amperage) is determined by the resistance of the nut.
So when you tighten a bolt down, there is some amount of "grunt" factor. The tighter the bolt, the more effort you have to put in turning the wrench, more grunt. Grunt equals power which is measured in watts, in the nuts and bolts world grunt is measured as torque, a measure of the power needed to overcome the resistance of metal tightening on metal. So in electronics Watts is the amount of power used for the voltage to make it through the resistance of the circuit and back to the battery.
Continuity - a one-word way of saying the circuit is complete. A circuit is nothing more than the path electricity has to take, just like a path people use to run around the neighborhood. So in electricity the current has to go from the battery, through the wires to a device (light bulb, black box, sensor, etc) and back to the battery; just as in the neighborhood you run down the streets and eventually get back to where you started, a complete path.
Now when we tighten a bolt our brain tells us how much power to use, either we read the torque gage or we sense how tight it is from the feelings in our hands and arms. In electrical circuits it is different. Even though 12v is there, and a battery may have several hundred amps of force available, electrical components are designed to use only so much current, only what they need in other words. That is probably the hardest thing for people new to electronics to understand. So lets see if this makes sense to you as an example.
Think of the gas tank as a battery, and the fuel is the current (amperage). If we put an Oklahoma credit card (siphon tube) into the gas tank we can think of the tube as a wire. Now when you get on the other end of the siphon tube you are playing the part of the electrical device (bulb, module, etc). If you are smart you only suck enough on the tube to get the gas flowing. In other words you only suck as much as you need to. That's basically what electronic devices do, they only use as much as they need (normal operation).
Instead of a torque wrench we use a multi-meter, so called because it measure multiple things (AC volts, DC volts, Ohms, and small levels of current (Amps) usually). Basically there are two types of multi-meters (hereinafter called a meter) analog and digital. An analog meter has a face and the meter needle moves across the face which has one or more scales written on it, much like the voltmeter on the e-glide. A digital meter reads out the result in digits. For the shade tree mechanic it makes no difference which you have, nor does it make any difference how much it costs. A Radio Shack $9.95 meter will work on the bike just as well as a $900.00 Fluke.
Some digital meters are auto-ranging. All that means is that the meter determines the amount of voltage/current being measured and sets the meter internally to read it, automatically. Otherwise you have to select the range you expect to measure, always set the range switch to a higher voltage than you will have in the circuit.
Some meters have the leads hard wired and others you have to insert the leads into jacks. One of the jacks will be labeled with a -, or GRD, or COM, or be painted black, or some combination of these. Obviously you put the black lead in this jack. The red lead you put into the jack that corresponds to what you are going to measure, AC, DC, ohms, or amps. Some meters combine these functions.
AC Volts: The only time on a bike you will use this setting is to measure the output of the stator and a couple of sensors (the sensors actually return a pulsating DC -the only way to measure it is as ACV without using a scope). AC, while it does in fact have polarity, polarity is not something we have to be concerned about when using the meter. Just set the range sw higher than the expected voltage and put the tips of the leads on the two pins of the stator output. AC is never measured to ground on the bike.
DC Volts: All other voltage on a bike is DC and DC voltage does have polarity. Black goes to ground and red goes to the spot you expect voltage to be. Again set the range sw higher than 12v.
Amps: Generally speaking you will never have occasion to use this setting. Most meters only measure very small amounts of current and require adapters to measure the type of current you might be concerned with if dealing with the coil. But if you decide you need to use it to measure amps, you must open the circuit and put the meter in series with the circuit. In other words the wire from the source part of the circuit goes to the black lead, and then the red lead goes to the load side of the wire that continues the circuit. Which color lead you use for source and load makes no difference, the meter is reading the flow of electricity.
Ohms: You will hear people call this aspect of using the meter by several names: ‘ohms check', ‘continuity check', and ‘ohm it out' are just a few. Keep in mind the circuit that voltage has to make, battery - device - battery, that circuit is what we check when we ‘ohm it out'. The meter has an internal battery. Never have voltage applied to the circuit you are testing when running an ohms check - never. The battery inside the meter sends out a small voltage on the test leads. Initially before putting the meter on a circuit of the bike you should cross the tips of the leads. When you do this the meter will read zero, showing that the circuit is complete - the internal battery voltage is able to make a complete circuit from the battery though the meter to one lead to the other lead and back to the battery.. On analog meters there is an adjustment so you can make so the meter needle will read exactly zero when crossing the tips of the leads. This is called ‘zeroing the meter'. Basically what you are doing when you zero the meter is adjusting the response of the meter to the strength of the battery.
When you ohm out something you should have the meter range set to R*1 (Resistance times 1). All this means is that the actual resistance of the circuit will be shown, unless the actual resistance is higher than the max shown on the meter face. If the meter needle does not move at all, change the range setting to a higher one (R*100, R*1K, etc), if you run up the range scale and the meter does not move at all, and the zeroing check was good, then there is an open circuit. No continuity in other words.
An open circuit (no continuity, infinite resistance) is shown by the meter needle not moving in an analog meter. When the meter needle does not move it indicates that there is infinite resistance, so much resistance that the voltage can not go through the circuit and return to the battery. On a digital meter an open circuit is generally shown by a line going up and down on the left side of the readout. When you turn on a digital meter in the ohms position and the leads are not crossed the display will show an open circuit, if you are not familiar with the readout of the meter this is the time to look at it and see how that particular meter displays infinite resistance.
On this meter the AC scale is in red and takes its numbers from the first scale just below it, the DC scale. Just like with ohms, the reading on the scale is multiplied by the range setting sw.
Just below the red AC scale are 4 scales for DC volts. Depending on which range setting you use, depends on which arc of numbers you read from. Other meters don't separate the DC scales the way this one does. If there is just one scale for DC then just as the AC scale was multiplied by the range switch setting, the DC scale is also multiplied by the range switch setting.
Looking at the DC scales you can see that the max reading (far right of scale) is 10 on the lowest scale, so with this meter you would have no choice but to put the range switch on 50 and use the meter on 12v circuits.
Schematics: The road map of wiring. Connectors are labeled with an A and a B side to show they go together. So connector 2A is connected to 2B on the bike, and in the schematics connector 2A may be on one page and connector 2B will be on another page. In schematics you will see lines crossing, if the lines have a dot at the intersection it means they are connected. Now you have to realize that the connection you see on the paper is not the location of the connection on the bike. No one splices connections in the middle of a wire. Electrically the connection drawn on the paper can be anywhere in that circuit.
Voltage, for our purposes, is everywhere in the circuit, immediately, when the switch is thrown, and that's why the actual point of connection is immaterial.
There are various ways to make schematics more user friendly. Some folks take the time to trace each circuit using a different color, others completely redraw the circuit leaving out the wires and connectors that are not in that one circuit so they end up with specialized schematics. I find it helps me to mark the schematics with a pen showing 12v when the ignition sw is on and ground on the connectors.
Relays: A relay is nothing more than an electronic switch. Basically it is composed of two distinct parts which need to be examined differently. Harley uses a relay that is packaged in a cube, other manufacturers may use a different packaging but the function is the same. Harley's relays have a pinout like the pic on the left and the electrical wiring diagram for the relay is on the right.
So to trouble shoot this relay you need to first make sure it energizes. Find out what switch applies 12v to pin 86, (the + side of the coil), put your meter red lead on pin 86 and the black lead on chassis ground. Make sure the meter is set to DCV and a range higher than 12v. Turn on the ignition sw and use the switch that applies voltage to the relay - the meter should read 12v if the switch is working properly, and there should not be 12v when the sw is not being used.
Typically you can hear and feel the relay energize.
The other half of the relay is the switch contacts (pins 30, 87 and 87a). The switch contacts are used to power a load, that allows very small diameter wire to be used to control the switch since energizing the relay uses a very small current. (The more current the heavier the wire). So pin 30 should have 12v on it all the time with the ignition sw on, and may have a heavier gage wire depending on the load characteristics.
Measure pin 30 and if it has the voltage, energize the relay and measure pin 87 to see if the switch part of the relay is working. If it is, when energized, the voltage will be connected to pin 87.
Some circuits will use pin 87a to pass voltage to a circuit when the relay is not energized and when the relay is energized the voltage is changed to some other circuit using pin 87, or if the voltage is not needed when the relay is energized pin 87 will be empty. You have to study the circuit to determine which situation is being used.
Some relays may have more than one set of contacts, Harley doesn't use them - yet - but if you run across one it operates the same. Each set of contacts is pulled when the relay energizes, just troubleshoot each set of contacts individually.
Note: The smaller diameter the wire is the higher the gage number. An 18 gage wire is smaller in diameter than a 6 gage wire.
Keep in mind that since relays use very small amounts of current to energize, it follows that there is not much resistance in the coil. So if you decide to ohm out a relay's coil you must put the meter on the R*1 scale or the meter will show a short and you may think the relay is bad when it is not. (The higher the scale the closer to zero the meter will read for very low amounts of resistance.) The same hold true for light bulbs, low resistance.
Sensors: Sensors are generally two or three wire devices. Sensors accept an input voltage(could be voltage, voltage and ground, or two different voltages) and depending on what and how they measure they send back a different voltage. Only studying the schematics and reading the shop manual for a description of how the sensor works will allow you to troubleshoot its' operation.
Fuses: Nothing more than a wire encased in plastic that is designed to melt (break) at a certain level of current flow. When the circuit it feeds draws too much current, the fuse blows. Fuses do not get old and blow for no reason. Keep in mind that a fuse feeds many individual circuits, or branches of a circuit so check your schematics.
Troubleshooting a blown fuse: One side of the fuse has 12v all the time, and if the fuse is not in place, the other side of the connector the fuse fits in has no voltage. The fuse allows voltage to pass to the other side. Pull the fuse, and use a meter to measure which side of the fuse connector has voltage. Set the meter to measure ohms and put a meter lead on the side that DID NOT have voltage and the other lead to chassis ground. The meter should show a short, a short is what causes a lot of current to flow and blows the fuse. Look in the schematics to see what that fuse feeds and start disconnecting things until the meter no longer reads a short. What ever you disconnected that stopped the short, there is the problem and you have to work on that particular circuit from that point on.
Another way, some think is easier, is to connect a bulb across the fuse and watch for the bulb to go off when the short is disconnected. I use both methods (depending on how I feel I guess) and to make it easier to use a bulb here is what I did one day in the shop. Take a blown fuse, or blow a good one, and using a dremel or razor knife cut the plastic off the ends of the fuse to reveal the metal ends of the spades. Then drill a hole in each end.
This bulb holder is for an 1157 tun signal/running light bulb. I wanted max resistance when using this to check for shorts so I wired both filaments to the same input on the fuse. That's why you can see two wires to one side and the ground wire to the other side. When in use both filaments light up and it is nice and bright.
Once I checked it to make sure it worked, I put silicone around the wiring to give it some sort of rigidity and protect the wires from being broken off.
Keep in mind that if you disconnect a cable connector, you may very well interrupt the flow of voltage to and from the item you are wanting to work with. This is especially true for the cable connectors that feed the handlebar switches. I use the technique in the following pic to measure a wire at the connector itself. Be careful, it is easy to short something out. Open a safety pin and insert the pin into the connector at the wire you are interested in measuring, then measure the voltage on the pin itself when you have all the switches on that need to be to send voltage on that wire.
It is really a bad idea to push a pin through the insulation of a wire to measure voltage, but if you really feel you have to do it, after you are done put some silicone on the puncture mark to prevent corrosion from starting inside the wire.
It is surprising how many experienced techs forget that cables have two ends. Everyone knows that corrosion is bad for a battery and tend to keep the terminals clean, but do yourself a favor and make sure the other ends of the battery cables are also free of corrosion and tight.
Every once in awhile you run into a real head scratcher - voltage is there and it still doesn't work. When that happens to you, and it will, start checking grounds. You can check grounds by putting the red lead on a known good 12v source and use the black lead to check for ground. Keep in mind that ground is often passed via the wiring harness, not all components use the frame ground. This is where the use of safety pins comes in handy to measure ground in cable connectors.
Some sensors pass ground to a light bulb or module. Typically the neutral switch does this, the neutral bulb has 12v all the time on one side and the sw passes ground which causes the bulb to light. The temp sensor is another one, but it passes resistance to ground, so current flows from the battery to the meter and then to the sensor. Inside the senor, between the input wire and chassis ground is a variable resistor, the more heat the resistor senses the less resistance it puts in the circuit to ground and the meter moves higher (less resistance more current flow). (Yes yes I know, all you electronic wizards are shaking your head and saying it is not a variable resistor, true, but this explanation is easier to understand, and understanding is more important than esoteric theory, especially since the sensor either works or it doesn't.)