Electronic Ignition System Diagnostics

Here at The Bonneville Shop we walk people through electronic ignition system diagnostics on a regular basis, after all there are very few professional shops willing to work on a motorcycle more than 10 years old.  Since anything electrical can be controversial I want to give the reader a brief overview of my background and qualifications before I get into this blog. 

I had the normal healthy fear of electronic components when I enrolled in Motorcycle Mechanic’s Institute in the summer of 1990, little did I know how much that would change over the years.  Not only did I get over that fear, but I became a fan of electronic fuel injection.  My career in motorcycle dealerships resulted in certifications from multiple manufacturers, and that financed my obsession with vintage motorcycles and cars. 

The testing procedures in this blog apply to the following ignition systems: Lucas RITA, Boyer-Bransden, Pazon Sure-Fire, Sparx, Wassell Vape, Tri-Spark (all Classic ignition systems), the stock ignition system used in most (carbureted) Triumph’s that came out of the Hinckley factory, and the stock electronic ignition systems for most carbureted 4-stroke motorcycles intended for street use.  The wire color codes may change from manufacturer to manufacturer, but the function and tests are still the same.

PLEASE NOTE:  This blog does NOT apply to AC ignitions systems.  Examples of AC ignition systems are CDI, magneto (Lucas K2F, Morris, etc.), and energy transfer ignition systems (5 wire Lucas stators).  AC ignition systems function and test in a different manner, and these differences have the potential to cause unnecessary confusion and electrocution.

Function of Electronic Ignition Systems

The basic function of any of the electronic ignition systems available from The Bonneville Shop is similar to a contact points ignition system.  With the points closed the electricity flows through the primary winding of the coil, building up a magnetic field.  When the points open the sudden loss of electricity in the primary winding collapses the magnetic field, which produces high voltage current in the secondary winding (HT side) through magnetic induction (aka-produces spark). 

An electronic ignition functions the same way, inside the black box (or Tri-Spark stator plate) there is a transistor that opens and closes like a set of points.  When the system is powered on the electricity flows through the primary windings, then through the transistor to ground to build up the magnetic field in the coils. 

When the magnets imbedded in the rotor pass by the pick up coils on the stator plate it sends an electrical pulse that causes the transistor to open like a set of points, causing the magnetic field in the coils to collapse and create a spark.  Some electronic ignitions use a “halls effect generator” type of pick up coil (TBS-0002A Tri-Spark ignition for triples and Lucas Rita are examples of this), the test for the pick up coil is slightly different for these ignitions.

We edited the diagram from the Wassell Vape installation guide to include the transistor.  To keep it simple and better explain its function I left out the additional capacitors and resistors.  Electricity flow from the positive ground, through the coils, through the transistor like it does through a set of 4CA/6CA points and out the white wire to the battery to build a magnetic field.  When the pick up coils send a pulse to the red wire, also known as the transistor base, it interrupts the flow through the transistor just like when your contact points open up.

Testing Functionality

There are two ways to test the functionality of transistors for electronic ignitions.  One is with a multimeter with a transistor testing port, however this does not always work due to the additional resistors and cannot be done on Tri-Spark ignitions due to the internal pick up coil circuits.  To do this you plug the red wire into the B (base) port, the black wire into the C (collector) port, the white wire into the E (emitter) port, and connect the pick up coil (stator plate) wires together.  A green light on the NPN side means it’s good.  The other method, which is more thorough is written out below.

The three main tools needed for electronic ignition troubleshooting are a fully charged battery, analog test light (non-LED), and a decent multimeter.  A non-LED test light is needed because polarity does not matter with incandescent bulbs.  I prefer an analog multimeter because the needle movement tells me more than a digital readout that relies on a polling rate.

Known good coil(s) are also necessary for testing the transistor in an electronic ignition system.  With a multimeter on the lowest resistance setting the reading should be between 1.7-1.9 ohms across the positive and negative (primary) terminals of Lucas 17M6 type ignition coils (PN 47275), these should be wired in series with 12V charging systems.  The resistance for 6V coils in series should be 3.3-3.8 ohms, same resistance as a single 17M12 type coils (PN 47276).  

Then we need to turn the multimeter up all the way to check the HT side of the coil, the spark plug lead to the positive terminal should be around 5000 ohms, this reading may vary by 1000 ohms depending on the meter used.  The primary side of dual lead coils should read close to what is advertised (ex: 3.5-3.7 ohms for TBS-3586). 

With a dual lead coil disconnected there should be no continuity between the high tension and primary sides (OL/infinite resistance), and there should be the same readings from primary to ground and HT to ground.  The high tension side resistance for dual lead coils offered from The Bonneville Shop should read no less than 7,500 ohms from spark plug lead to spark plug lead with spark plug caps off.

A no spark condition is generally caused by bad coils which is why we check those before diagnosing the electronic ignition module or pick up coils.  Other causes are bad power delivery to the coils and/or ignition unit (black box/Tri-Spark stator plate).  The following tests should be done in order of power delivery to the ignition system using a test light grounded to the battery.  To keep this topic on vintage motorcycles I am addressing positive ground for the following tests. 

1. Grounding/earthing points are at the top of the list. Rust, corrosion, and paint are electrical insulators. With the positive battery terminal connected/grounded to the motorcycle, clip the test light on the negative battery terminal and make sure it’s nice and bright when probing all the grounding points used by the ignition system. Move onto the next steps after all grounding points are good, solid and clean.
2. Ignition switch/key switch: The test light should turn on and off with movement of the key/switch when the battery is connected. If it does not, disconnect the ignition power wire and check again (white wire on Lucas equipped motorcycles). If the test light comes on/off with ignition power wire disconnected the fault is farther along in the system.  For an intermittent fault check, gently tap on the switch, this checks the contact of the internal brushes and springs.  If the ignition switch tests good, move onto the next step.
3. Handlebar kill switch: These became a mandatory safety item in 1971 and are a great idea since slides can stick and intakes can leak. Points and electronic ignition use a normally closed switch for the power to pass through it on the way to the coils and/or ignition module, so it’s the second check with the test light. Disconnect the white/yellow wire coming out of the switch and connect it to the test light.  With the ignition switch on the test light should go out every time the switch is placed in the off position (or kill button pressed).  If the light comes on every time the button is pressed, you are attempting to use a normally open kill switch for AC ignition systems, and it will not work correctly. This is another component to tap on to check for intermittent contact of the internal brushes and springs. These are prone to failure and can be bypassed (not recommended since this is a safety item).  If the switch test good, move onto the next step.
4. Next we need to make sure the ignition module is getting power, this needs battery voltage. For Boyer-Bransden, Sparx, and Wassell Vape this will be power to the white wire. Black/yellow on Tri-Spark.  White/yellow on Lucas Rita (negative ground). Less than battery voltage indicates a faulty switch or faulty wiring.

If all the above tests passed and connections are solid it is time to test the resistance of the pick up coils on the stator plate.  The resistance should be between 120-140 ohms for most transistorized ignitions with no continuity to ground.  This is between the black/white and black/yellow wires going to the stator plate on Boyer-Bransden, Pazon Sure-Fire, Sparx and Wassell Vape.  Systems that use a “halls effect generator/reluctor” pick up coil like the Lucas RITA will have lower resistance readings (with no continuity to ground) since they are energized when in use.

The last test in this blog can also be the first test of the ignition system, and it is the only way to test the pick up coil in a Tri-Spark Classic’s ignition system.

1. Remove the spark plugs, place them inside spark plug caps and make sure the threaded/ground electrodes are touching metal on the head.
2. Remove the stator plate and rotor from the timing cover and camshaft.
3. Connect the wires to the stator plate.
4. Turn on ignition switch.
5. Hold the stator plate in one hand.
6. Use your other hand to pass the magnets in the rotor past the pickup coils.
7. The spark plugs should produce spark each time the magnet passes by the pick up coils.

The halls effect generator/reluctor type pick up coils like the Lucas RITA and Tri-Spark original triples ignitions (TBS-0002A) can be tested with the rotor left in the motorcycle.  A spoke or screwdriver can be used to trigger the pick up coil to produce spark.  This spoke method can be used to diagnose the ignition systems on modern Triumph’s and many other makes of motorcycles that use a reluctor with the pick up coil.

If your electronic ignition passes all the above testing, the problem is in the timing or mechanical condition of the engine.  For electronic ignition timing instructions please read Dave Porter’s blog on using a timing degree wheel.