The late electric starter circuit is probably the most complicated circuit on these old Honda motorcycles. We often see parts of the original circuit bypassed or not functioning right but just like every other circuit on these motorcycles, when broken down it is nothing more than a few wires and switches that make it up. Similar to the headlight circuit, Honda has an early (Pre 1973) and a late (Post 1974) version of this electric starter circuit. In this article, we are going to focus on the late versions of the circuit that have safety switches. What that means is that the electric starter cannot be engaged when the motorcycle is in gear. It must be either in neutral or have the clutch lever pulled for the start button to engage the starter motor. Certain versions of these motorcycles also include an always-on headlight that will turn off temporarily when the starter motor is engaged. 

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Compatible models with this instructional
Early Style Safety Switch Circuit Models
CB360T / CL360 K1
Later CB360T with the always-on headlight
CB550 K0-K1* (used the starter motor safety unit)
CB750 K3-K5* (used the starter motor safety unit)
Late Style Safety Switch Circuit Models
CB500T
CB550K (1976 and up)
CB550F
CB750K (1976 and up)
CB750F
CB200T* (used a unique version of the late style circuit)

 

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. 

 

Earlier Style of the Starter Solenoid Safety Switch Circuit

Explanation of circuit path

In this explanation, we will be going over the circuit beginning from two different ground points as the circuit can ground from either safety switch or both at the same time. 

Ground connection through the clutch lever safety switch: Ground goes from a green wire on the harness and connects to the dark green wire with red stripe when the clutch lever is pulled in. This gaurentees that the starter motor is not engaged when you are in gear. 

Ground connection through the Neutral safety switch: Ground goes through the neutral light switch from the metal body of the engine and leaves on the light green wire with red stripe when the transmission is in nuetral. This circuit the splits with one half moving on to the neutral light (we cover this circuit in our neutral light circuit troubleshooting) and the other half going to the starter circuit. The light green wire with red stripe connects to a one way diode and the to the same dark green wire with red stripe from the clutch safety switch. The one way diode prevents the neutral light from using the clutch lever safety switch as a ground light. Without it, the neutral light would turn on everytime the clutch lever was pulled.

The activation side of the starter solenoid: Both of the dark green wires with red stripe connect together and run to the starter button in the right handlebar switch. When the starter button is depressed, current will travel out of the right handlebar switch on the yellow wire with red stripe. Finally, the yellow wire with red stripe runs back to the starter solenoid to complete the ground activation side of the solenoid. The solenoid is connected directly to the black 12v positive circuit so the activation circuit will immediately trigger when the starter button is pushed and either of the safety switches are connecting to ground. Now this activation side is only one side of testing the starter solenoid. A solenoid is simply a switch that triggers a switch so in this case the activation side is there to trigger when the main starter wires connect to the battery to engage the starter. 

The connection side of the starter solenoid: When the activation side of the starter solenoid is triggered by the depression of the start button and grounding of either the neutral switch or clutch safety switch, the starter solenoid will bridge the current between the 2 large posts on the top of the starter solenoid. This connects the positive cable that runs from the battery to the solenoid directly to the positive cable that runs down the frame, under the engine, and up to the positive bolt on the electric starter. The starter motor grounds through the metal casing directly to the engine and then will engage, turning over the engine. 

 

Earlier style using the “starter motor safety unit"

The CB550 K0-K1 and CB750 K3-K5 used a modified version of this circuit that uses a specialized “starter motor safety unit” in place of the one-way diode. This starter motor safety unit appears to be a complicated circuit board that does the same task the one-way diode does. Since the starter motor safety units are extremely difficult to find, you should be able to convert to the one-way diode version of this circuit fairly easily using our simplified wiring diagrams above. Cut the connector off the harness and cap off the black 12v positive wire, ground wire, and yellowwire with red stripe as they will not be used anymore. The diode will then be installed between the light green wire with red stripe and the dark green wire with red stripe. Be sure that the light green wire with red stripe still connects to the light greenwire with red stripe running to the neutral light in the gauge cluster. The dark greenwire with red stripe also still needs to be connected to the dark green wire with red stripe running to the clutch handlebar switch. 

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Troubleshooting Tests

Testing the clutch lever safety switch

1. Unplug the dark green wire with red stripe that connects the clutch safety switch to the main harness inside the headlight bucket.

2. Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.

3. Connect the alligator clip on the test light to the dark green wire with red stripe that goes to the clutch safety switch. Touch the probe end of the test light to a known good 12v positive black wire in the headlight bucket.
4. With the key switch set to the run position, squeeze the clutch lever. The test light should kick on with the lever pulled in and indicate a working clutch safety switch. 

 

Potential issues: 

The test light does not turn on when the clutch lever is pulled in - It is most likely that you have a bad switch and will need to replace it. This switch is the same as our front brake light switch but the replacement will have different color wires. When installing our new switch, it does not matter which wire is plugged in and where. As long as one wire is plugged into ground and the other into the dark green wire with red stripe then it will function properly. 

 

One other issue that can happen is the switch gets installed into the clutch perch incorrectly. The switch has a small pin that is normally held closed when the clutch lever is inactive. When the lever is pulled, it releases the pin and activates the switch. If the switch body is pushed too far in or out of the perch housing, it can always stay on or never turn on. 

 

Testing the diode and neutral 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 diode from the wiring harness connector. 
3. Connect the alligator clip on the test light to the positive side of the battery.
4. With the bike in neutral, touch the probe on the test light to the light green wire with red stripe terminal on the wiring harness. The test light will kick on and indicate a working neutral switch. If it does not, refer to our neutral light troubleshooting video right here.
5. Using a jumper wire, connect one pin on the diode to a known good ground point. 
6. With the test light alligator clip still connected to the positive terminal on the battery, touch the probe to the other pin on the diode. 
7. If the test light does not kick on, connect the ground jumper wire to the other pin on the diode and touch the test light probe to the opposite pin. The test light should only kick on in 1 out of 2 of the setups and indicate that current is only able to travel through in one direction. 

 

Potential issues: 

The test light does not turn on when testing the diode in either direction - The diode will need to be replaced.

The test light turns on when testing the diode in both directions - The diode will need to be replaced.

 

Testing the starter button 

1. Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.

2. Remove and unplug the yellow wire with red stripe and the dark green wire with red stripe that goes to the right handlebar switch.
3. Use a jumper wire to connect the dark green wire with red stripe to a known good ground point.
4. Connect the alligator clip on the test light to the positive side of the battery or a known good 12v positive black wire. If using a black 12v positive wire, be sure that the key switch is set to the run position and the kill switch is turned off to prevent the coils from charging during testing.
5. Touch the probe end of the test light to the yellow/red wire running to the right handlebar switch and depress the start button on the switch. If working properly, the starter button will turn on the test light only when depressed.  

Potential issues: 

The test light does not turn on when depressing the start button - You could have two problem areas. First is the yellow wire with red stripe or dark green wire with red stripe that run inside the handlebars to the right switch. The wires could have a break inside the handlebars or at the solder connection to the small pad that contacts the button in the right handlebar switch. The second area would be an issue with the button. When the button is depressed, it has a small pin in it that makes contact with a pad and can wear down to the point that the internal pin no longer touches the pad. We have new smaller buttons available if this is the case. 

 

The test light does not turn off when releasing the start button - Somehow you are grounding the yellow wire with red stripe without pressing the starter button. It is not uncommon for the handlebar switch wires to develop shorts where they enter and exit the inside of the handlebars. Friction over the years can rub through the protective housing and the wire could be grounding against the handlebars. 

 

Testing the 12v positive connection to the yellow wire with red stripe

1. Unplug the yellow wire with red stripe going to the right handlebar switch from its connection to the yellow wire with red stripe on the main harness.
2. Connect the alligator clip on the test light to a known good ground point. 
3. With the key switch set to the run position, touch the probe to the yellow wire with red stripe connection on the main harness. The test light should kick on and indicate a good 12v positive connection from here through the solenoid and back to the positive side of the battery.

 

Potential issues: 

The test light does not turn on when testing for 12v positive at the yellow wire with red stripe coming from the main harness - Move on to testing the starter solenoid trigger wires. If those are working properly then you likely have a break in the yellow wire with red stripe somewhere in between the starter solenoid and headlight bucket in the main harness.

 

Testing the ground connection to the dark green wire with red stripe

1. Unplug the dark green wire with red stripe going to the right handlebar switch from its connection to the dark green wire with red stripe on the main harness.
2. Connect the alligator clip on the test light to a known good 12v positive point. 
3. With the key switch set to the run position, touch the probe to the dark green wire with red stripe connection on the main harness. The test light should kick on and indicate a good ground connection from here when the bike is either shifted into neutral or the clutch lever is pulled in. 

 

Potential issues: 

The test light does not turn on when testing for ground at the dark green wire with red stripe coming from the main harness - If the safety switches were working properly, then you likely have a break in the dark green wire with red stripe somewhere in between them and the right handlebar switch in the main harness.

 

Testing the starter solenoid trigger wires for continuity

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 yellow wire with red stripe on the starter solenoid by the battery from the main harness.
3. Connect the alligator clip of the test light to the ground connection of your battery.
4. Turn the key switch to the run position. 
5. Touch the probe end of the test light to the inside of the yellow wire with red stripe connector on the starter solenoid. The test light should kick on and indicate both a good 12v positive connection and continuity through the solenoid trigger circuit.

 

Potential issues: 

The test light does not turn on when testing the yellow wire with red stripe - If you have a good 12v connection at the black wire that runs to the starter solenoid then there is likely an internal issue with the starter solenoid and it will need to be replaced.

 

Testing the starter solenoid main contacts

1. Before unhooking any larger positive wires on the starter solenoid, always unhook the negative wire from the battery to prevent electrical shock to yourself and the motorcycle.
2. With the battery negative disconnected, disconnect the large wire that runs under the engine and to the electric starter from the post on the starter solenoid. 
3. Reconnect the ground wire to the battery.
4. Push the start button. You should hear an audible clicking from the starter solenoid whenever the start button is depressed to prove that it is working. 
5. Connect the alligator clip on the test light to the ground of the battery and touch the probe end to the post on the electric starter that you disconnected. 
6. Press the start button. The test light should kick on alongside an audible click and signify that the solenoid is also properly transferring the 12v positive current from the ground down to the starter motor. 

 

Potential issues: 

The test light does not turn on and/or an audible click is not heard when depressing the start button - There is likely an internal issue with the starter solenoid and it will need to be replaced.

 

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Later Style of the Starter Solenoid Safety Switch Circuit

Explanation of circuit path

In this explanation, we will be going over the circuit beginning from two different ground points as the circuit can ground from either safety switch or both at the same time. 

Ground connection through the clutch lever safety switch: Ground goes from a green wire on the harness and connects to the dark green wire with red stripe when the clutch lever is pulled in. This gaurentees that the starter motor is not engaged when you are in gear. 

Ground connection through the Neutral safety switch: Ground goes through the neutral light switch from the metal body of the engine and leaves on the light green wire with red stripe when the transmission is in neutral. This circuit the splits with one half moving on to the neutral light (we cover this circuit in our neutral light circuit troubleshooting) and the other half going to the starter circuit. The light green wire with red stripe connects to a one way diode and the to the same dark green wire with red stripe from the clutch safety switch. The one way diode prevents the neutral light from using the clutch lever safety switch as a ground light. Without it, the neutral light would turn on everytime the clutch lever was pulled.

The activation side of the starter solenoid: Both of the dark green wires with red stripe connect together and run to the starter solenoid to complete the ground side of the activation side of the solenoid. The biggest difference between this later style circuit and the early covered above is that the activation of the starter solenoid is trigger by its 12v positive connection, not ground. Since these motorcycles have an always on headlight, black 12v positive runs directly to the starter button on the right handlebar switch and connections directly to black wire with red stripe that connects to the headlight circuit. This means when the key is on, the headlight is on. 12v positive connection is disconnected from the black wire with red stripe and connected to the yellow wire with red stripe when the starter button is pressed, which carries 12v positive connection down the the other side of the starter solenoid. The headlight and starter motor are the 2 largest draw items in the electrical system on these motorcycles, so Honda setup the circuit in this manner to temporarily redirect as much current as possible to the electric starter while the motorcycle is starting. Once you let go of the starter button, the circuit returns to its previous state with 12v positive going directly to the headlight circuit. We cover this circuit much more in our The Three Fuse Headlight and Running Light Circuit (Post 1974 Late Style): Electrical Troubleshooting and Basics on a Vintage Honda Motorcycle article. 

The connection side of the starter solenoid: When the activation side of the starter solenoid is triggered by the depression of the start button and grounding of either the neutral switch or clutch safety switch, the starter solenoid will bridge the current between the 2 large posts on the top of the starter solenoid. This connects the positive cable that runs from the battery to the solenoid directly to the positive cable that runs down the frame, under the engine, and up to the positive bolt on the electric starter. The starter motor grounds through the metal casing directly to the engine and then will engage, turning over the engine. 

 

CB200T specific version of this circuit

The CB200T uses an always-on headlight circuit so it shares the positive activated start button with the late style of this circuit. However, there are no safety switches installed on the ground side of the circuit so the motorcycle can be accidentally started while in gear. The black wire coming off the starter solenoid connects directly to the green ground wires to ground it. This is the only one-off example we have seen of this style with the motorcycles we support.

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Troubleshooting Tests

Testing the clutch lever safety switch

1. Unplug the dark green wire with red stripe that connects the clutch safety switch to the main harness inside the headlight bucket.

2. Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.

3. Connect the alligator clip on the test light to the dark green wire with red stripe that goes to the clutch safety switch. Touch the probe end of the test light to a known good 12v positive black wire in the headlight bucket.
4. With the key switch set to the run position, squeeze the clutch lever. The test light should kick on with the lever pulled in and indicate a working clutch safety switch. 

 

Potential issues: 

The test light does not turn on when the clutch lever is pulled in - It is most likely that you have a bad switch and will need to replace it. This switch is the same as our front brake light switch but the replacement will have different color wires. When installing our new switch, it does not matter which wire is plugged in and where. As long as one wire is plugged into ground and the other into the dark green wire with red stripe then it will function properly. 

 

One other issue that can happen is the switch gets installed into the clutch perch incorrectly. The switch has a small pin that is normally held closed when the clutch lever is inactive. When the lever is pulled, it releases the pin and activates the switch. If the switch body is pushed too far in or out of the perch housing, it can always stay on or never turn on. 

 

Testing the diode and neutral 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 diode from the wiring harness connector. 
3. Connect the alligator clip on the test light to the positive side of the battery.
4. With the bike in neutral, touch the probe on the test light to the light green wire with red stripe terminal on the wiring harness. The test light will kick on and indicate a working neutral switch. If it does not, refer to our neutral light troubleshooting video right here.
5. Using a jumper wire, connect one pin on the diode to a known good ground point. 
6. With the test light alligator clip still connected to the positive terminal on the battery, touch the probe to the other pin on the diode. 
7. If the test light does not kick on, connect the ground jumper wire to the other pin on the diode and touch the test light probe to the opposite pin. The test light should only kick on in 1 out of 2 of the setups and indicate that current is only able to travel through in one direction. 

 

Potential issues: 

The test light does not turn on when testing the diode in either direction - The diode will need to be replaced.

The test light turns on when testing the diode in both directions - The diode will need to be replaced.

 

Testing the starter button 

1. Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.

2. Remove and unplug the yellow wire with red stripe that goes to the right handlebar switch.
3. Connect the alligator clip on the test light to a known good grounding point.
4. Touch the probe end of the test light to the yellow wire with red stripe running to the right handlebar switch and depress the start button on the switch. If working properly, the starter button will turn on the test light only when depressed.  

Potential issues: 

The test light does not turn on when depressing the start button - You could have two problem areas. First is the yellow wires with red stripe that run inside the handlebars to the right switch. The wires could have a break inside the handlebars or at the solder connection to the small pad that contacts the button in the right handlebar switch. The second area would be an issue with the button. When the button is depressed, it has a small pin in it that makes contact with a pad and can wear down to the point that the internal pin no longer touches the pad. We have new smaller buttons available if this is the case. 

 

Testing the ground connection to the yellow/red wire

 

1. Unplug the yellow wire with red stripe going to the right handlebar switch from its connection to the dark green/red on the main harness.
2. Connect the alligator clip on the test light to a known good 12v positive point. 
3. With the key switch set to the run position, touch the probe to the yellow wire with red stripe connection on the main harness. The test light should kick on and indicate a good ground connection from here when either the bike is shifted into neutral or the lever lever is pulled in. 

 

Potential issues: 

The test light does not turn on when testing for ground at the dark green wire with red stripe coming from the main harness - If the safety switches were working properly, then you likely have a break in the dark green wire with red stripe somewhere in between them and the right handlebar switch in the main harness.

 

Testing the starter solenoid trigger wires for continuity

6. Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.
7. Unplug the yellow wire with red stripe and dark green wire with red stripe on the starter solenoid by the battery from the main harness.
8. Connect the yellow wire with red stripe to a known good 12v positive connection using a jumper wire.
9. Connect the alligator clip of the test light to the ground connection of your battery.
10. Turn the key switch to the run position. 
11. Touch the probe end of the test light to the inside of the dark green wire with red stripe connector on the starter solenoid. The test light should kick on and indicate both a good 12v positive connection and continuity through the solenoid trigger circuit.

 

Potential issues: 

The test light does not turn on when testing the dark green wire with red stripe - There is likely an internal issue with the starter solenoid and it will need to be replaced.

 

Testing the starter solenoid main contacts

7. Before unhooking any larger positive wires on the starter solenoid, always unhook the negative wire from the battery to prevent electrical shock to yourself and the motorcycle.
8. With the battery negative disconnected, disconnect the large wire that runs under the engine and to the electric starter from the post on the starter solenoid. 
9. Reconnect the ground wire to the battery.
10. Push the start button. You should hear an audible clicking from the starter solenoid whenever the start button is depressed to prove that it is working. 
11. Connect the alligator clip on the test light to the ground of the battery and touch the probe end to the post on the electric starter that you disconnected. 
12. Press the start button. The test light should kick on alongside an audible click and signify that the solenoid is also properly transferring the 12v positive current from the ground down to the starter motor. 

 

Potential issues: 

 

The test light does not turn on and/or an audible click is not heard when depressing the start button - There is likely an internal issue with the starter solenoid and it will need to be replaced.

 

One last note

After finishing your testing of the starter circuit, it's important to remember that just because the starter circuit might be working doesn’t guarantee that the starter motor or starter motor clutch is working to turn the engine over. Refer to our rebuild guides below to learn how to rebuild your starter motor and starter motor clutch.

 

How to Rebuild your Electric Start on your Vintage Honda Motorcycle

Electric Starter Clutch Rebuild / Removal (For Kick Start Only) : Honda CB350 / CB360 / CB450