I wrote this piece for the /5 group to address a problem that one of the riders
had with his turn signals. They were acting very strangely. This was
not intended to be a "recipe" type of advice, but an explanation into why some
of the anomalies occurred.
The description of the inconsistent turn signal flashing is typical of a
grounding problem. Grounding is simply a term for the electrical system on one
"side" of a circuit. It is made up of the same stuff as the "other" side of a
circuit, namely resistance. We tend to think of resistance as a fixed thing.
That is so often not the case and it is very easy to get confused.
I will use simple terminology, not the stuff that our engineers will like. I
have little choice but to use my "farmer" type explanations. I
hope that this helps my intended readers, but it may offend the technical types.
We will slowly build a simple turn signal circuit. Lets start with a simple
bulb as an example. The bulb is a 12 v and rated at 12 watts. The power law
tells us that 12 watts at 12 volts will have a current flow of 1 ampere, or amp. Volts (12) times amps (1) is the power in watts. 12 X 1=12.
If in fact we discovered that the circuit actually had 2 amps flowing then we
would be consuming 24 watts of power.
The resistance that the bulb would actually have would be defined by Ohms
law. The current equals the voltage divided by the resistance, or I =
E/R. In this case the resistance would be one Ohm.
Here is where it starts to get interesting. If you put your multimeter on the
bulb to measure the resistance, you would be very surprised. It wouldn't measure
anything close to one Ohm. How can that be?
We incorrectly assumed that the resistance is linear. It often isn't. The multimeter doesn't use 12 volts to test resistance. It uses much less.
At a lower voltage, the resistance is quite different.
For our next example we are going to use a more accurate type of multimeter
called an oscilloscope. This is nothing more than a voltmeter that uses a
TV screen to show us what happens to the voltage and current each small part of
a second, often dividing it much closer than a millionth of a second.
We would like to think that since electricity is fast (moving at the speed of
light) that as soon as we throw the switch on our simple circuit with only one
bulb in it, the current would instantly come up to one amp. The TV screen would
show zero volts and then rise up to 12 volts. We would have a "square"
jump at the bottom and again at the top of the 12 volts.
We would quickly find that something else happens. It would start up quickly
(not quite square, but close) and when arriving at the top it would take forever
to finally get to 12 volts. It is very rounded off at the top. It takes 1/4 of a
second to get there. Observation of the bulb also confirms that the bulb
doesn't get to full brightness instantly, but there are more factors to explain
The bulb actually starts off at a very low resistance and as current goes
through the "business part" of the bulb, the resistance actually climbs up a
lot. The resistance is affected by the heat in the wire. The
resistance isn't linear with respect to heat (voltage X current).
Now we add in a "flasher" to make the bulb turn on and off. It is nothing
more than a special type of switch. The flasher is (the older original type) a
metallic strip of metal that heats up and turns on or off a switch. The higher
the current, the faster it heats up and then turns off. It cools down and makes
contact again. The "cycle" repeats itself.
So now we have a bulb that is nonlinear in operation. We have attached it to
a switch that we have wanted to be nonlinear. We now have a more complicated
situation. We then add in another bulb for the other end of the motorcycle. The
total current drawn by the two bulbs is what now controls the flasher. A
flasher that is correct for one amount of current, will be quite different for
Our next addition to the circuit is two more bulbs for the other side of the
motorcycle to make up a "right and left" indicator for traffic to see. This
requires a "turnsignal" switch and associated wiring. Our flasher will "see"
either the right side circuit or the left side circuit, but not both at the same
time. Next we add in another bulb for the driver to see as an indicator. We are
starting to have a complicated system. We haven't even started talking
about a 4 way flasher or cancel system.
To reduce the production costs, we can sort of "cheat" a bit. We have to run
copper (read expensive) wires "out" to the 4 turn signals. We don't need to run
a return circuit back if we just "ground" them. Just let the metal of the
motorcycle carry the current back. This is where we start getting into
At each connection to ground (metal of the frame) we have two metals in
contact that aren't of the same material. This is an invitation for trouble. With moisture and odd chemicals getting into the contact, we can end up with
some totally unpredictable connections. In extreme cases it can be a very simple
radio frequency transmitter. It is more common for the connection to be
nonlinear. That means that while the resistance of the connection should be
zero, it will actually be some real amount and not fixed. It will change, sort
of like the bulb, but not in a predictable way. It will seem to have a
mind of its own.
Think of all of the places where we have connections on our 30 year old
machines. Each is potentially a problem, not just the return side.
That is why a special grease can do wonders for keeping out the moisture and
oxygen that start the errant chemical processes.
With so many connections changing resistances so easily, it is quite
challenging for a non electrical person to diagnose them by using a common
The most common solution to turn signal defects is to run a separate ground
wire from the turn signal housing back to a ground.