Originally Posted by AMF Ironhead
I was checking the electric diagram for my 1980 XLH in my Clymer manual and it has a "ground to handlebar screw" that I do not see in my bike at all. Anyone knows about ground wire to the handlebar screw? Also, how can I check for ground problems? I don't even know what should be ground.
Sorry for for all this, just trying to fix the sucker and learn.
I'll give a basic in electricity.
It's probably just a jumper wire from the frame to the handlebar, to make sure the ground path doesn't have any resistance. Resistance is anything that doesn't let electricity flow well, like a rubber bushing, or wood, or air. Electrons like to move thru good, naked metal. Copper, steel, etc.
Resistance is measured in numbers called "ohms". A reading of "0", or zero, ohms, is the best number to get if you are checking for ground. The higher the number, the more resistance. The more resistance, the less the electricity will move. You need a multi-meter to measure this.
For example, you would set the meter up to read ohms, put one lead on the negative post of the battery, and one lead on the triple tree. Unless there is a gasket or bushing somewhere in the middle, the meter should read about zero.
"Ground" is also the same as the negative post on your battery.
All circuits need to have a complete path. Electrons go out from the battery, some get used up, and the unused ones come back to the battery.
There is another little concept to understand, and it's called "potential". That kind of means, how ready is the battery to do it's job. Use the multi-meter again, this time set to read DC voltage.
If you put the multi-meter between the positive and negative battery terminals, you are reading available voltage, or the "potential" it has to do it's job. If it only reads 2 volts, it has no potential to get the job done.....it's too weak. If it's 12-14 volts, it has full potential, it's ready to go.
So, now that we know about resistance and potential, you can figure out just about anything.
Let's take potential, and put it in a practical application.
There is a wire going from the positive post of the battery to the ignition switch. If you measure the voltage there, you will see it has the same voltage as if you measured it at the battery. That is the potential. When you turn the ignition switch on, the potential goes to different places, like up to the light switch.
The headlight won't come on yet, because the potential is just sitting behind the switch, waiting for you to turn the switch on. As soon as you turn the switch on, the potential flows thru the switch and to the headlight bulb.
It flows thru the filament in the bulb. Will the headlight light up? It depends.
Remember how I said electrons go out, some get used, and some come back to the battery? They come back thru "ground". That is the flow path. That is why a good ground is critical. It is the return part of the flowpath.
The other side of the light bulb is connected to the steel part of the headlight bucket. The headlight bucket is connected to the forks with steel bolts. The forks are connected to the frame, via the neck. If the neck were plastic, the electricity couldn't make it back to the battery, and the light would not light up.
But, we know that the neck is not plastic. But, at many places on the bike there are rubber bushings, plastic widgets, etc. Sometimes extra ground wires are used to make sure there is always a good return path so the electrons can find their way home to the battery.
Here are two examples of how to check something. Let's say the headlight won't light up. Crap. Get out the multi-meter.
1) Put the meter on ohms. Take out the lightbulb. Put the leads on the bulb at the connection points (sometimes little gray dots). If the meter gives no reading, the bulb filament is broken, and no electricity can go across. Filaments will have some resistance, maybe a few ohms. If the meter read, say, 10 ohms, the bulb is ok. Next step.
2) Put the meter on voltage. Turn the key on, turn the headlight switch on.
Put the black lead to a good, known ground spot on the bike. Put the positive lead on the terminal inside the light connector. Should read voltage.
If there is voltage in the bucket, and the headlight would not come on, it's probably an issue on the return path, possibly a ground issue (maybe a corroded connector on a ground connection).
If there is no voltage in the bucket, then you would need to move backward
and check for voltage at the headlight switch.
Anyway, there you have it. An overview of electricity, discussion of ground path, potential, ohms, resistance, meter usage, and how to break a troubleshooting problem in half, decide which half the problem might be on.