The neutral light circuit is yet another simple circuit on a vintage Honda motorcycle that we receive tons of questions about. While the 12v positive side connects straight to the indicator bulb, it is the grounding path and neutral light switch that baffles most. On nearly every motorcycle we support you will find the neutral light switch under the chain cover, a spot that also sees more dirt and grime than anywhere else on the motorcycle. This exposure to dirt often leads to a malfunctioning neutral light switch. Fortunately, simple cleaning and testing can most often resolve any issues you might be having with this switch or other parts of the circuit. In this video, we are going to help you understand the basics of the factory Honda neutral light circuit wiring and how to individually test each component to discover what is at fault and what works as it should.
The Simplified Honda Neutral Switch Diagram
Since current flows from negative to positive, it is important to start at ground when tracing any circuit. If you have watched our ground circuit explained video, you will know that most metal on these motorcycles is ground. In this case specifically, ground starts with the engine and makes contact when the transmission switches into the neutral position. The circuit travels from the neutral switch on a light green wire with red stripe to a white plastic harness connector. This connector is shared with the pink, white, and yellow wires from the charging stator. Once through the harness connector, the circuit travels up to the headlight bucket and to the neutral indicator light bulb. Current leaves the light bulb on the 12v positive black wire connection which as we know, goes back to the key switch and then the positive side of the battery.
*1975-Later Motorcycle Owners: Some of the models such as the CB360T and later four cylinder models mixed the neutral indicator light circuit with a clutch safety switch circuit. The basic layout and function of the circuit remains the same, just with a tie in to the starter solenoid circuit. Refer to our late style starter solenoid/clutch safety switch circuit video for more information on why this is tied together.
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.
Testing the neutral light switch ground
- The neutral light switch will be located underneath the left side chain cover.
- Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.
- Unplug the 4-pin wiring harness connector that contains the light green/red neutral switch wire and the yellow, white, and pink wires from the stator.
- Connect the alligator clip on your test light to the positive terminal on the battery.
- Touch the probe to the light green with red stripe wire inside the harness connector.
- The test light should be on when the transmission is in neutral and turn off when any other gear is selected with the shifter.
Potential issues:
Test light not turning on: Corrosion, dirt and debris, or a broken wire could be causing the wire and neutral light switch to not be ground properly. Disassemble the switch and clean everything. Check that there is a solid connection from the wire to the neutral light switch.
Test light will not turn off: The light green wire with red stripe is likely is chaffed or broken and grounded on another piece of metal outside of the switch.
Testing the 4-pin wiring harness connector
- Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.
- Plug the male and female sides of the plastic wiring harness connector containing the light green with red stripe wire, yellow wire, white wire, and pink wire.
- Connect the test light alligator clip to the positive battery post.
- Use the probe to touch the light green with red stripe wire as it exits the back of the plastic wiring harness connector heading towards the headlight bucket.
- The test light should be on when the transmission is in neutral and turn off when any other gear is selected with the shifter.
Potential issues:
Test light not turning on: There is a bad spade connector or corrosion build up inside the plastic 4-pin harness connector. Cut off the existing connector, strip the wires to expose fresh copper, crim on new spade terminals, and install a new plastic harness connector.
Testing 12v positive power to the neutral indicator light
- Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.
- Find the black 12v positive wire that runs to the gauge cluster and unplug the wire from the large black bundle it is plugged into. This is usually inside the headlight bucket.
- Connect the test light alligator clip to ground.
- Turn on the ignition switch on the motorcycle and touch the test light probe to the location that the black 12v positive wire was plugged in to.
- The test light will illuminate if you are getting the proper 12v positive power at this connection.
Potential issues:
Test light not turning on: Refer to our understanding 12v positive connection video linked at the top of this article. You either have an issue with the 12v positive circuit on the motorcycle or a bullet connector full of corrosion.
Testing the neutral indicator light
- If the 12v positive black connection tested good in the previous test, start by plugging it back in and unplugging the light green wire with red stripe that runs up to the gauge bulb cluster. This is usually located inside the headlight bucket.
- Touch the light green wire with red stripe to ground.
- Turn on the ignition switch.
- The indicator bulb should immediately light up in the gauge cluster.
Potential issues:
Neutral light indicator bulb does not turn on: It could be as simple as a burnt-out bulb. Other issues could be a break in the wires that run to the gauge or corrosion in the bulb socket that needs to be cleaned up.
Parts to Buy: