Honda motorcycles from roughly 1974 and on incurred many specific changes to comply with worldwide safety regulations. Many of the changes were aimed at increasing visibility on the road and safety when operating a motorcycle. The easiest way to tell if your motorcycle falls in this "later" category is from the inclusion of a 3-fuse fusebox on the motorcycle. Earlier motorcycles used a single 15amp fuse for the entire motorcycle whereas later motorcycles used a 15amp main fuse and 7amp or 10amp fuse on the headlight and taillight circuits. In this article, we will cover how Honda set up the headlight and running light circuits on these motorcycles and how to troubleshoot every electrical part and wire within it.

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Compatible models with this instructional
CB200T
CB360 / CL360 / CJ360
CB550K / CB550F
CB750K3 and up / CB750F
CB350F / CB400F
Most Honda models from 1974 on.

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: Only briefly 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 they are active and charging. If left on too long the coils will overcharge and be ruined. 

Explanation of circuit path

In this explanation, we will be going over the circuit in reverse. If you have seen our ground circuit video, you will know that a circuit starts at ground. While the current flows from negative to positive, it is not always the most simple way to explain it. In the case of the headlight circuit, starting at the single connection to 12v positive in the right handlebar switch and branching our way to the various splits that make up the headlight and running light circuit on your vintage Honda will be easier to follow. 

12v positive to the right handlebar switch: Current begins with the black 12v positive wire that runs into the right handlebar switch. The right handlebar switch on these motorcycles acts as a junction for several different functions. While we show an on/off switch in our diagrams, these motorcycles could have come with either an on/off right handlebar switch or an always on switch. Both versions will function the same in the circuit. If you have an on/off switch, in the on position, the black 12v positive wire connects both to the black wire with red stripe and the brown wire with blue stripe. With the always on switch, the black 12v positive wire is immediately connected to both the black with red stripe and brown with blue stripe wires right when the keyswitch is turned on.

The Fuse Box: Both the black wire with red stripe and brown wire with blue stripe run down the spine of motorcycle to a 3 fuse fusebox either under the side cover or next to the battery box under the seat. The black wire with red stripe connects to either a 7amp or 10amp fuse. Current exits the "head" fuse on a black wire with yellow stripe and heads towards the left handlebar switch. The brown wire with blue stripe connects to either a 7amp or 10amp fuse in the fusebox as well. Current exits the "tail" fuse on a brown wire with white stripe. At this point the brown wire with white stripe will mirror the setup and wiring of the early style of this circuit. If you need to troubleshoot the taillight or gauge running lights refer to our specific taillight circuit video or the early headlight circuit video that includes how to diagnose and test the gauge running lights.

The black wire with yellow stripe: The black wire with yellow stripe exits the fuse box and runs back up the spine of the motorcycle to the left handlebar switch.

The left handlebar switch: Inside the left handlebar switch the black wire with yellow stripe splits to connect to both the white high beam wire and blue low beam wire. When set to L(low beam) on the switch, current exits on the white wire and run straight to the low beam filament on the headlight. The headlight bulb will then connect to the green harness ground connections inside the headlight bucket. When set to H(high beam) on the switch, current exits on the blue wire and immediately splits. One blue wire will run to the high beam filament on the headlight bulb while the other will run to the high beam indicator bulb. Both bulbs will ground through the green harness ground connections inside the headlight bucket. 

The front turn signal running lights: The last part of the circuit entails the light blue wire with white stripe and the orange wire with white striple that exit the left handlebar switch and power the front running lights inside the front turn signals. We will go more in-depth on this portion of the circuit late in this article. 

Troubleshooting Tests

Testing the headlight bulb

1. Remove and unplug the white, blue, and green connections that go to the headlight to remove the lens and bulb for testing. 
2. Using a known good battery, connect a jumper wire from the ground post of the battery to the green ground wire going to the headlight bulb.
3. Connect another jumper wire to the positive side of the battery and touch the other end of the jumper to the white wire to test the low beam on the headlight. Be careful to not let the positive jumper wire touch any ground point on the motorcycle or headlight. If the low beam filament kicks on then the low beam filament works properly. 
4. Touch the positive jumper wire to the blue wire to test the high beam on the headlight. If the low beam filament kicks on then the high beam filament works properly.

Potential issues: 

The low beam filament or the high beam filament on the headlight does not turn on - The headlight bulb needs to be replaced. If you are still using the stock sealed beam headlight lens, you will need to upgrade to our H4 compatible lens that allows you to use brighter H4 halogen and LED headlights and replace just the bulb down the road. 

Testing the right 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. Locate where the right handlebar switch connects to the main harness on your motorcycle. For most motorcycles, this should be underneath the tank or inside the headlight bucket. 
3. Connect the alligator ground of the test light to a known good ground point.
4. Test the black wire(s) going to the right handlebar switch by touching the test light probe to the inside of the black connector. Turn the ignition switch to the run position. The test light should kick on and signify a good 12v positive connection. 
5. Unplug the black/red wire and touch the probe to the inside of the black/red connector coming from the right handlebar switch. Turn the ignition switch to the run position. Turn on the headlight if you have a headlight on/off switch on your motorcycle. The test light should kick on and signify a good 12v positive connection. 
6. Unplug the brown/blue wire and touch the probe to the inside of the black/red connector coming from the right handlebar switch. Turn the ignition switch to the run position. Turn on the headlight if you have a headlight on/off switch on your motorcycle. The test light should kick on and signify a good 12v positive connection. 

Potential issues: 

The test light does not turn on when testing black - Refer to our positive circuit guide.

The test light does not turn on when testing black/red and brown/blue - You could have a broken or torn wire in the handlebar switch wires inside your handlebars, dirty contacts inside the switch, or a broken solder joint inside the switch that connects the wire to the internal contacts.

The test light does not turn off when testing black/red and brown/blue - (only applicable if you have a headlight on/off switch) If you turn off the headlight switch but still get power out on the black/red wire then someone has either wired something incorrectly or put the contacts back together wrong. 

Testing the fuse box

1. Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.
2. Locate the fuse box on your motorcycle. For most motorcycles, this should be underneath the seat or inside one of the left or right side covers.
3. Connect the alligator ground of the test light to a known good ground point.
4. Turn the ignition switch to the run position. Turn on the headlight if you have a headlight on/off switch on your motorcycle.
5. Touch the probe end of the test light to the black/red wire terminal that holds the “head” fuse. The test light should kick on and signify a good 12v positive connection. 
6. Touch the probe end of the test light to the brown/blue wire terminal that holds the “tail” fuse. The test light should kick on and signify a good 12v positive connection. 
7. Touch the probe end of the test light to the black/yellow wire terminal that holds the other side of the “head” fuse with the fuse connected. The test light should kick on and signify a good working fuse and 12v positive connection. 
8. Touch the probe end of the test light to the brown/white wire terminal that holds the other side of the “tail” fuse with the fuse connected. The test light should kick on and signify a good working fuse and 12v positive connection. 

Potential issues: 

The test light does not turn on when testing the black/red terminal - If the right handlebar switch was working, then you could have a break on the black/red wire that runs through the main harness. The brass terminal on the wire could also be full of corrosion and need to be replaced. 

The test light does not turn on when testing the brown/blue terminal - If the right handlebar switch was working, then you could have a break on the brown/blue wire that runs through the main harness. The brass terminal on the wire could also be full of corrosion and need to be replaced. 

The test light does not turn on when testing the black/yellow terminal - The fuse could be faulty and need to be replaced or the wire terminal could be corroded and not making proper contact with the fuse. 

The test light does not turn on when testing the brown/white terminal - The fuse could be faulty and need to be replaced or the wire terminal could be corroded and not making proper contact with the fuse. 

Testing 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. Locate where the black/yellow left handlebar switch connects to the main harness on your motorcycle. For most motorcycles, this should be underneath the tank or inside the headlight bucket. 
3. Connect the alligator ground of the test light to a known good ground point.
4. Turn the ignition switch to the run position. Turn on the headlight if you have a headlight on/off switch on your motorcycle.
5. Disconnect the black/yellow wire and touch the test light probe to the inside of the black/yellow connector on the main harness. The test light should kick on and signify a good working fuse and 12v positive connection.
6. Locate the blue and white connections inside the headlight bucket and unplug them from the headlight.
7. With the left handlebar switch set to low, touch the test light probe to the inside of the white connector. The test light should kick on and signify a good working fuse and 12v positive connection. Set the switch to Hi and then touch the test light probe to the inside of the blue connector. The test light should kick on and signify a good working fuse and 12v positive connection.

Potential issues: 

The test light does not turn on when testing the black/yellow - You could have a break on the black/yellow wire which runs through the main harness. The bullet terminal on the wire could also be full of corrosion and need to be replaced. 

The test light does not turn on when testing the white - You could have a broken or torn wire in the handlebar switch wires inside your handlebars, dirty contacts inside the switch, or a broken solder joint inside the switch that connects the wire to the internal contacts.

The test light does not turn on when testing the blue - You could have a broken or torn wire in the handlebar switch wires inside your handlebars, dirty contacts inside the switch, or a broken solder joint inside the switch that connects the wire to the internal contacts.

Diagnosing the brown/white gauge light circuit & high beam indicator circuit

Refer to our early-style headlight circuit video to learn how to troubleshoot the gauge bulbs and sockets on your motorcycle.

Refer to our taillight circuit video to learn how to troubleshoot the taillight circuit on your motorcycle.

The Front Running Light Circuit

What are the front running lights on your Honda?

Due to safety regulations in the US, Honda implemented front running lights on the majority of their motorcycles from 1974 on. This means that the front turn signals had dual filament bulbs in them much like the taillight so when the headlight was on, so was a dimmer filament inside the turn signals. This was done in an effort to increase motorcyclists' visibility on the road.

A generalized explanation of the circuit path

Honda set this circuit up in many different ways over the years so there is not one exact method that things are connected to make these work both inside and outside of the switch. 

Grounding: Ground begins through the metal body of the turn signal. Since the headlight buckets are mostly plastic on these motorcycles, Honda grounded the metal bodies of the turn signals by using a special grounding nut that attached the turn signal body to the headlight ears. These nuts are unique and have a solded dark green wire on them that plugged into the harness ground circuit. 

12v Positive: Ground then traveled from the metal body of the dual filament bulb to the dimmer of the two filaments. Current exits the dimmer filament on either the light blue wire with white stripe or the orange wire with white stripe. These wires then travel up to the left handlebar switch where they connect in various ways to a 12v positive connection from the black wire with yellow stripe. 

Our three ways to “fix” the running lights

1.  Troubleshoot the issue by figuring out how to fix the stock wiring and setup for your specific running lights.
2. Plug the light blue/white and orange/white wires directly into a black 12v positive wire inside the headlight bucket so they turn on with the key switch. Certain Honda models were wired that way directly from the factory anyway.
3. Disable the running lights altogether so they function just as turn signals.