Lets take a look at what happens in most cars (not all).  The bulb in the "tail light" has two elements.  One element is for the running lights or tail lights.  This element is always on when your light switch is on.  The turn signal switch and also the brake switch use the second element in the bulb.  This second (and brighter) element comes on when you turn your signal on to turn left or right.  That sounds simple enough.
Now, when you put your brakes on, the second elements (the brighter ones) in both of the right and left lights come on.  The electronic circuit sends power to both signal lights at the same time and both left and right lights come on.   This circuit also controls the signal light and the brake light together, so that you can signal and turn while your brakes are on.   So, count the wires and you have:  1. tail,  2. left/stop,  3. right/stop, and 4. ground.  A total of 4 wires. 

Now lets take a look at how a motorcycle works.  A motorcycle does not have this electronic circuit to control the brakes and signals like that. Most motorcycles have one centrally located brake light and two signal/tail lights; one on each side of the bike. The tail/brake light is usually a dual element bulb. (Two elements inside one bulb)
When the brakes are applied, only the brake light comes on.  When you signal a turn, only the signal light comes on.  That sounds simple enough. A motorcycle has one wire to the right signal, one wire to the left signal and one wire to the brake light and one wire to the running/tail lights.
Count left, right, brake, tail and ground and you get five wires on the motorcycle, controlling the three lights on the back.  (left, right, brake/tail and ground)   
If your trailer has only two lights on the back, then you require a converter.  If your trailer has a set of lights for your signals and tail lights and a separate set of lights for your brakes, then you do not require a converter.  

An electronic converter will take the 5 wires found on a motorcycle and convert them to 4 wires for your trailer.  When you apply the brakes, the power from the brake wire is split and sent to both signal lights on the trailer.  It also prevents cross flow of power from one signal to the other when you turn a signal on.
Trace wires in motorcycle harness and identify each one for function.  NOTE:  Not all manufacturers use the same wire color code.  Consult your owner’s manual or motorcycle service department.

After all wires on motorcycle have been located and identified, the wire ends of the converter can be spliced as follows:

Green – Right Turn Signal
Red – Stop Lamps
Yellow – Left Turn Signal
Brown – Tail or Running Lights
White – Ground

                                        How does an Isolator work?

OK. Let’s not talk about Watts, Amps, Volts, right now.  Let’s start with a really simple example.

Have you ever used an extension cord to power a large appliance or tool?  After a while the cord starts to get warm and then hot.  If the tool is big enough, the cord will become too hot to touch and then it could actually melt.  Put a fuse into the system and the fuse is supposed to melt first. (Blow)

The extension cord was designed to handle only a certain size appliance.  If you overload it, then it will get hot.  This is how a toaster works.  Overload the small wires and they get hot and toast the bread. (The twist in the wire also helps it to heat up, but that is for another lesson)
The wires on your motorcycle are designed to handle all the lights on the bike with a little bit of safety cushion.   Put too many lights on the system and the wires will get hot, or you will blow a fuse.  Or if you have a computer or ABS and the fuse is too big, you might blow something in the computer or ABS before the fuse blows.

Realistically, the computer and ABS should be adequately protected from other electrical circuits.

An Isolator is a separate system that connects directly to the battery and then sends power to the extra lights on your trailer.  It is “isolated” from your bikes normal wiring.  

The Isolator is connected to the 5 wires on the bike that control the lights for 1.Brakes, 2.Running, 3.Left Turn, 4.Right Turn and 5.Ground.  These Isolator wires take very little power from the bike; only enough to trip the relays in the Isolator.  When you press your brake pedal, the relay trips inside the Isolator and power for the trailer’s brake lights comes right from the battery and not through the bikes wiring harness.  The same thing happens for running, left and right turn lights.

The wires on the Isolator are heavier than most wires on the bike, so it will be able to handle the extra load required by the lights on the trailer.  The Isolator should have an inline fuse also.


If your TRAILER wires are not the standard colors.


Do the following in exact order and you will not cause any undo sparks or burnouts.

Always wear safety glasses when working with a battery.

Use a spare battery.  Clamp a wire from the negative post of the battery to the trailer frame.

Now using a test light, connect the wire from the test light to the positive post of the battery.

Touch the probe of the test light to the frame.  It should light up.  If it doesn’t light, check all connections.

Touch the probe of the test light to each wire on the trailer wiring harness, one at a time until the test light lights up. 

This is your ground wire. 

NOTE:  If the test light comes on when touching more than one wire, then there is a short circuit.  The wire is bare somewhere and is touching the frame.  This must be corrected before continuing.

NOTE:  The test light should only light up when touching one of the wires.

Unhook everything.

Clamp the ground wire that you found to the negative post of the battery.

Clamp a jumper wire to the positive post of the battery.  Do not let it touch the frame of the trailer.

Use the jumper wire from the positive post of the battery and touch it to each of the other wires.

Record and mark the wires as to what lights up when each wire is touched. 

For example running, stop and left or right signal lights.

Connect isolator to the trailer wires as follows:

                Yellow wire from isolator to Right Turn Signal
               Brown wire from isolator to Left Turn Signal
               Green wire from isolator to Tail or Running Lights
               Blue wire from isolator to Brake Lights
               Black wire from isolator to Ground wire.

By doing it in this order you will not cause any undo sparks or burnouts.

Do you still have questions not answered here?  Send me an e-mail and I will try to give you an answer.

Jim Victor:     PullingYourTail@gmail.com