The turn signal circuit is by far the circuit we get the most questions on. When broken down to its core concepts, it might actually be one of the most simple. Take away the flasher relay and you have a simple on-and-off circuit that you can fully test and troubleshoot with the help of a test light and solid battery. In this article, we are going to help you understand the wiring concepts, circuit layout, and troubleshooting techniques for getting your flashers flashing and your blinkers blinking.

The Simplified Honda Turn Signal Circuit Diagram

(Applies to the Honda CB175 / CB200 / CB350 / CB360 / CB450 / CB550 / CB750 family of motorcycles)

Current flows from negative to positive so we always start our circuit with the ground path. If you have seen our ground circuit explanation video, then you will know that most parts are ground simply to any metal part of the frame, turn signals included. Honda factory turn signals do not use a ground wire connected straight to the bulb socket but instead ground through the metal body of the turn signal housing. Front turn signals ground from the metal body to the metal headlight ear which carries ground to the headlight bolt, into the headlight bucket to a nut that is directly wired to the dark green ground circuit. For the rear turn signals, they can be set up one of 2 ways. Either the turn signals are bolted to a bracket that is directly bolted to the frame or it rubber mounted and uses a ground wire from the body of the turn signal to the dark green ground circuit. The positive connection comes from each turn signal on a light blue or orange wire to a four way connection either inside the headlight bucket or under the gas tank. Honda setup the motorcycles that use a single turn signal indicator to connect between these orange and light blue connections, more information on how this functions below. Coming out of the four way connections, a single light blue (right circuit) wire and single orange (left circuit) wire run to the left handlebar switch selector. The current leaves the handlebar switch on the gray wire and runs directly to the flasher relay. Finally, the other side of the flasher relay is connected directly to the black wire 12v positive side of the motorcycle harness and eventually make it back through the kew switch and back to the positive side of the battery.

*1975 and later motorcycle owners: Your motorcycles have the possibility of using dual filament front turn signals that give them a running light that turns on with the headlight in addition to the turn signal light, much like how the taillight operates. While this running light is inside the turn signal bulbs, it is a very different circuit that is tied to the later style headlight circuits and thus is covered in that article. 

The Single Turn Signal Indicator Light

From the factory, Honda setup the majority of its motorcycles are this time to use a single turn signal indicator bulb for both the left and right turn signal circuits. Because incandescent bulbs can turn on with current traveling in both directions, they did not wire the turn signal sockets with a specific positive and negative side. The indicator light bulb simply used which ever turn signal circuit that was not currently on to pull its ground through. This has caused some confusion when people have switched to a modern LED bulb for the turn signal relay as LED bulbs will only allow current to flow in one direction. Watch the video below as we go more in depth and show how to use our supplied diode to adapt this part of the circuit to work with an LED bulb.

Important: Ensure you have read our positive and ground explanation articles and watched the videos before diving into this troubleshooting. You will need a known good battery and test light to troubleshoot your ignition system wiring. 

Understand the Positive Circuit on a Vintage Honda Motorcycle

Understanding the Ground Circuit on a Vintage Honda Motorcycle

Warning: Always turn the ignition switch on with the kill switch set to the off position to test it. When turned on with the kill switch set to on / run the coils are active and charging. If left on too long the coils will overcharge and be ruined. 

Testing for 12v positive power at the flasher relay

1. Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.
2. Connect the test light alligator clip to the engine to ground it. 
3. Unplug the flasher relay from the black 12v positive wire and the gray wire. It can be located under the tank by the keswitch or someone around the battery box.
4. Turn on the ignition switch.
5. Touch the probe to the inside connection of the black 12v positive wire that was connected to the flasher relay.
6. The test light should turn on and signify a good 12v positive connection from that point all the way back to the positive side of the battery.

Potential issues:

Test light not turning on: See our Understand the Positive Circuit on a Vintage Honda Motorcycle article. Either there is a broken wire or something is wrong with the 12v+ circuit before it plugs into the flasher relay. 

From this test forward, remove the flasher relay from the circuit and simply jump the black and gray connections together with the jumper wire. Flasher relays are sensitive and can be easily burned out from shorts so get the circuit completely working before reinstalling it. 

Testing for 12v positive power at the gray wire before entering the left handlebar switch

1. Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.
2. Find the main harness gray wire connection where it plugs into the gray wire running to the left handlebar switch. This could be under the gas tank or inside the headlight bucket.
3. Connect the test light alligator clip to ground.
4. Turn on the ignition switch.
5. Touch the probe to the inside connection of the black 12v positive wire that was connected to the flasher relay.
6. The test light will illuminate if you are getting the proper 12v positive power at this connection and signify a good 12v positive connection from that point all the way back to the positive side of the battery.

Potential issues:

Test light not turning on: Usually will be a break in the wiring or a bad bullet connector. Use the test light to move further down the circuit, testing for 12v positive as you go by pushing the probe into the gray wire.

Testing for 12v positive power at the light blue and orange wires through the handlebar switch

1. Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.
2. Unplug the light blue and orange wires coming from the left handlebar switch. 
3. Connect the test light alligator clip to ground.
4. Turn on the ignition switch.
5. Touch the probe to the light blue bullet connection and click the handlebar switch to select the right side circuit. The test light will illuminate if you are getting the proper 12v positive power at this connection and signify a good 12v positive connection from that point all the way back to the positive side of the battery.
6. Repeat the test with the orange wire by touching the probe to the orange bullet connection and click the handlebar switch to select the left side circuit. The test light will illuminate if you are getting the proper 12v positive power at this connection and signify a good 12v positive connection from that point all the way back to the positive side of the battery.

Potential issues:

Test light not turning on: If you had the proper 12v positive power in the above test going to the switch, it is likely there is an issue inside the switch itself and it needs to be replaced or torn apart to clean the contacts. Another common issue is the wires that run through the handlebars can rub or break at the points where the enter or exit the handlebars. You would need to remove the left switch from the handlebars and either repair or replace the damaged wire. 

Testing the light blue and orange 4-way bullet connectors

1. Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.
2. Find the main four way connections where all of the light blue and orange wires meet. This could be under the gas tank or inside the headlight bucket.
3. Connect the test light alligator clip to ground.
4. Turn on the ignition switch.
5. Touch the probe to the inside light blue bullet 4 way connector and click the handlebar switch to select the right side circuit. The test light will illuminate if you are getting the proper 12v positive power at this connection and signify a good 12v positive connection from that point all the way back to the positive side of the battery.
6. Repeat the test with the orange wire by touching the probe to the orange 4 way connector bullet connection and click the handlebar switch to select the left side circuit. The test light will illuminate if you are getting the proper 12v positive power at this connection and signify a good 12v positive connection from that point all the way back to the positive side of the battery.

Potential issues:

Test light not turning on: Its possible you have a bad or dirty bullet connection from either the light blue or orange wires coming from the switch or a damaged 4 way bullet connector. 

Testing the turn signal indicator bulb

1. Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.
2. Find and unplug the light blue and orange wires that are a part of the gauge cluster wires. They will be in a bundle that also includes a dark blue wire (high beam indicator) and a light green wire with red stripe (nuetral light indicator).
3. Connect one of the turn signal indicator wires (either light blue or orange) to a known good black 12v positive wire in the headlight bucket (test this with a test light if you do not know if it is working or not). 
4. Turn on the ignition switch.
5. Touch the other turn signal indicator wire (either light blue or orange) to a good ground connection. 
6. The turn signal indicator bulb should illuminate.

Potential issues:

Indicator light not turning on: Its possible you either have a bad bulb in the indicator socket or it has been replaced at some point by an LED indicator bulb. See our LED indicator bulb video above for more information on what you need to do to get that working. Lastly, you could just have corrosion in the bulb socket or a tear in the wire.  

Testing the front turn signal bulbs

1. Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.
2. First test that both the left and right turn signal are grounding properly in the front. Connect the test light alligator clip to a known good black 12v positive connection (test this with a test light if you do not know if it is working or not), turn on the ignition switch, and touch the probe to the metal body of each turn signal. The test light should illuminate for each, indicating that you have a good ground connection for both turn signals.
3. To test the turn signal bulbs in the front left and right signals, find the light blue and orange wires that come from the turn signal body. They can also be black wires with a small light blue or orange sleeve on the end by the bullet connector. 
4. Connect each wire to a known good black 12v positive connection and turn on the ignition switch one at a time.
5. The turn signal bulb should illuminate brightly. 

Potential issues:

Turn signal light not turning on: Its possible you have a bad bulb in the turn signal at the simpliest solution. Other issues include corrosion in the socket itself or corrosion in between one of the spots where ground is transferring. The special nuts that are directly wired to the dark green ground circuit could also be missing and you will need to find a way to ground the headlight bolts to the ground circuit. 

Testing the rear turn signal bulbs

1. Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.
2. First test that both the left and right turn signal are grounding properly in the rear. Connect the test light alligator clip to positive side of the battery, turn on the ignition switch, and touch the probe to the metal body of each turn signal. The test light should illuminate for each, indicating that you have a good ground connection for both turn signals.
3. To test the turn signal bulbs in the rear left and right signals, find the light blue and orange wires that come from the turn signal body. They can also be black wires with a small light blue or orange sleeve on the end by the bullet connector. 
4. Connect each wire to a known good black 12v positive connection and turn on the ignition switch one at a time.
5. The turn signal bulb should illuminate brightly. 

Potential issues:

Turn signal light not turning on: Its possible you have a bad bulb in the turn signal at the simpliest solution. Other issues include corrosion in the socket itself or corrosion in between one of the spots where ground is transferring.

Testing the flasher relay

1. Flasher relays are best tested using a working turn signal because certain test lights do not draw enough current to trigger the older mechanical style turn signal relay. If you are testing a modern electronic turn signal relay, then you can use a test light. 
2. Connect a jumper wire from the positive side of the battery to the post on the turn signal relay marked either B or +. Connect the positive wire from the turn signal to the other post of the turn signal relay. If the turn signal is properly grounded then it should immediately start flashing. 
3. If the relay is not marked with a clear B or + post, then it is possible you might plug it it backwards to test it the first time. Certain mechanical turn signal relays will work regardless of how you have them plugged in, but electronic relays do not and have a specific direction they need to be hooked up. If the turn signal turns on, but does not flash then the connections are probably backwards and need to be reversed. 

Potential issues:

Turn signal light does not turn on AND flash: If the light turns on but is not flashing, then its likely that the relay is hooked up backwards as described in step #3. If the light is not turning on at all and does not work with the relay plugged in either way, then it will need to be replaced. 

Parts to Buy: 

Test Light

Mechanical Turn Signal Relay

Electronic Turn Signal Relay

Replacement CB175 / CB350 / CB360 / CB450 / CB500K Turn Signals

Replacement CB500T / CB550 / CB750 Turn Signals

Turn Signal Stems

Incandescent Turn Signal Replacement Bulbs

Incandescent Indicator Bulbs

CB350 / CB450 Left Side Handlebar Switch

CB360 / CB550 / CB750 Left Side Handlebar Switch