Like most of the circuits on a vintage Honda motorcycle, the ignition system circuit is incredibly simple. With basic knowledge of the circuit and a test light, you can diagnose issues and fix them to keep cruising down the road. In this article we are going to help you understand the basics of the factory Honda ignition system wiring and how to individually test each component to discover what is at fault and what works as it should.
The Simplified Honda Ignition System Diagram
(Applies to the Honda CB350 / CB360 / CB450 / CB550 / CB750 family of motorcycles)
Since current flows from negative to positive, it is important to start at ground when tracing this circuit. If you have watched our ground circuit explained video, you will know that most metal on these motorcyles is ground. In this case specifically, ground starts through the points plate on the engine and goes to the upper points pad. The circuit continues across the points pads, down the points spring, to the connector on the points wire, and up either the right (blue) or left (yellow) to plug into the right or left coil. Be sure that the left point, left ignition coil, and left spark plug are hooked together. The same goes for the right. For the 4-cylinder motorcycles of this era, refer to the ignition timing links are the bottom of this article for a specific breakdown of which point goes to which cylinders. Leaving the ignition coil, the current merges back together on the black / white wire to run to the kill switch. If the kill switch is set to on / run then current will exit the kill switch back 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. If you have an older CB350 / CB450 / CB750, then there is a chance you may not have a kill switch. In this case, once current exits the coils it will merge into a single 12v positive black wire connection immediately.
*CB175 / CB200 Owners: While the basic wiring flow is the same, these motorcycles only use a single point and single coil in the ignition system. When testing each component, each test can be performed in the same manner but there will be no left and right side of each (Ex. single point, single coil, no merging black/white wires). Be sure to test each spark plug lead coming off the one coil.
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 on / run 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 for continuity through the points
- Unplug the ignition point/s from the ignition coil.
- Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.
- Connect the test light alligator clip to the left or right points wire. Be sure the engine is rotated to a position where the point you are currently testing is closed.
- Touch the probe to the positive terminal of the battery and manually open the point you are testing.
- The test light should be on when the point is closed and turn off when the point is opened when everything is functioning correctly.
Potential issues:
Test light not turning on: Corrosion build up on the points pads, points spring to wire terminal or break in the points wire at some point. Ignition point pads will wear down over time and create pits or uneven surface contact. Use sandpaper or a points file to correct the issues in the pad surface to bring them back to parallel and remove corrosion. Replace if necessary.
Test light will not turn off: Something is causing your point to ground before the current gets to the point pad. A point wire terminal attached to the wrong place on the point can cause this. It should be bolted to the point and touching the point spring, but be separated from the point bracket with the insulation washers. The points wire terminal and point spring can also be touching the points plate or points cover on your engine, causing the current to go straight to ground before the point.
Testing for 12v positive power at the coils
- Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.
- Connect the test light alligator clip to the engine to ground it.
- Turn on the ignition switch and be sure the kill switch (if your motorcycle has one) is set to the on / run position.
- Use the probe to touch the Black / White wire connection that the coil/s connect to on the main harness (this connector will be black if you do not have a kill switch on your motorcycle).
- The test light will illuminate if you are getting the proper 12v positive power at this connection. Test it further by switching the kill switch on and off. If the test light turns off and on with the kill switch then your kill switch is working properly. Since current flows from negative to positive, if this is working that means you have a good 12v positive connection through the kill switch, back to the key switch, and back to the positive connection on the battery.
Potential issues:
Test light not turning on: Usually will be a break in the wiring, a bad bullet connector, or issues with the kill switch. Use the test light to move further down the circuit, testing for 12v positive as you go by pushing the probe into the black / white wire. If you get to the kill switch and still do not have 12v positive power on the black wires going to your handlebar switch, refer to our positive circuit troubleshooting.
Test light will not turn off with the kill switch: Either a bad kill switch, something wired incorrectly, or someone in the past has bypassed the kill switch in the wiring harness. Refer to the wiring diagram in the OEM Honda service manuals.
Testing for 12v positive power through the coils
- Test your test light by connecting one side to ground and touching the probe to the positive terminal of the battery.
- Connect the test light alligator clip to the engine to ground it.
- Turn on the ignition switch on the motorcycle with the kill switch set to on / run (if your motorcycle has one) and touch the test light probe to test the coil wire that connects to the points wires. If you have 2 coils, test both sides.
- The test light will illuminate if you are getting the proper 12v positive power at this connection.
Potential issues:
Test light not turning on: If you had the proper 12v positive power in the above test going to the coils, it is likely there is an issue inside the coil itself and it needs to be replaced. Use the test light probe to poke into the wire itself you are testing to verify that the issue is not a bad bullet connection. If you have power on the wire but not at the bullet connection, replace the bullet connection. If there is no power on either, replace the ignition coil.
Testing the functionality of the coils
- Start by disconnecting the ignition point/s from the coil/s.
- Remove the spark plug and plug it into the spark plug boot. Be sure the outside of the spark plug is grounding against the engine case as shown in the video.
- Connect a jumper wire to the coil where the points wires were plugged in.
- With the motorcycle ignition switch turned on and the kill switch set to on / run, take the not connected side of the jumper wire and scrape it against a ground point like the engine case.
- When the jumper wire touches ground, it completes the circuit and charges up the coil. Once that connection is broken, the jumper wire simulates the point opening and causes the primary winding of the coil to fire the spark plug. This allows you to test the primary windings in the coil outside of their connection to the spark plug. Test the other side point and coil if you have two. Make sure the jumper wire is connected to the proper right or left coil that you are trying to test.
- With both coils verified working, test the entire system by plugging the wires back into the ignition coils and turning the engine over with either the kick starter or electric starter. You should get a bright purple spark at the end of each spark plug.
Potential issues:
No spark: Make sure to use a known good spark plug and spark plug boot for this test. As you can see in the video it can be difficult to get it to spark on every strike this way, but you should get the spark plug to fire a few times to verify that it is working. If not, you likely have a bad primary winding in the ignition coil. Replace it.
Ignition Timing
As a final note, it is important to note that just knowing that you have spark is not enough to get the motorcycle to fire. The spark needs to also happen at the correct time, so be sure to check out our ignition timing video below that pertains to your specific model of motorcycle.
How do I set the ignition timing on my CB175 / CL175 / SL175 / CB200 / CL200?
How to set the ignition timing on the Honda CB350 / CL350 / SL350
How do I set the ignition timing on my CB360 / CL360 / CJ360?
How do I set the ignition timing on my CB450 / CL450 / CB500T?
How often do I need to set the ignition timing on my CB550K / CB550F / CB500K?
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