The electric starter circuit can be a more intimidating circuit to approach due to its inclusion of high voltage and a solenoid. With that said, when broken down it is nothing more than a few wires and switches that make it up. Similar to the headlight circuit, Honda has a early (Pre 1973) and a late (Post 1974) version of this electric starter circuit. In this article, we are going to focus on the early version of the circuit that has no safety switches. What that means is that the electric starter can be engaged when the motorcycle is in gear, causing it to lurch forward. 

Be sure to ALWAYS start your motorcycle in Neutral!

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Compatible models with this instructional
CB175 / CL175
CB200K / CL200
CB350K / CL350K / SL350 K0
CB360 K0 / CL360 K0
CB450K / CL450K
CB500 K0-K2
CB750  K0-K2
Most Honda models before 1973

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

Ground connection through the handlebars: Ground connection makes its way from the frame to the bottom of the handlebar riser with the help of a small jumper wire. Once on the handlebar riser, ground travels from the riser, to the handlebar, and to the right handlebar switch. When the starter button is depressed, current connects to the yellow wire with red stripe and then travels down the wiring harness to the starter solenoid next to the battery. 

The activation side of the starter solenoid: Once the yellow wire with red stripe arrives at the starter solenoid, it connects directly to a black 12v positive wire to complete the activation side of 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, 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. 

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Troubleshooting Tests

Testing the starter button and 12v positive connection to the yellow/red wire

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 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 set to off to prevent the coils from charging during testing.
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.  
5. Locate the other part of the yellow wire with red stripe that was unplugged and runs to the main harness. 
6. Connect the alligator clip on the test light to a known good ground point. 
7. With the key switch set to the run position, touch the probe to the yellow wire with red stripe connection. 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 depressing the start button - You could have three problem areas. First is the yellow wire with red stripe. The yellow wire with red stripe could have a break in it 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 will make contact with a pad. This pin can wear down to the point that it no longer touches the pad. We have new smaller buttons available if this is the case. The 3rd issue would be with your switch grounding. The OEM switches for these motorcycles ground using the switch body that transfers ground first to the chrome handlebars, then to the handlebar risers, then to a jumper wire that goes from the bottom of the riser to the gauge bracket, and finally the gauge bracket should be grounding through the triple tree to the frame of the motorcycle. The first main issue with grounding that can be found is that you are missing the crucial smaller jumper wire that grounds the handlebar riser to the gauge bracket. We cover this jumper wire more in-depth in our ground article. The other main issue is not having chrome handlebars. Stock handlebars were chrome so they were able to transfer ground current but if you have replaced your handlebars with a painted handlebar then you need to either remove the paint under the handlebar switches AND risers to transfer the ground current or run a separate ground wire to both the right and left handlebar switch bodies to ground them. 

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. 

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 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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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