How to check a Honda CT90 Ignition Coil

How to Check a Honda CT90 or CT200 Ignition Coil

Here is how I perform a basic check of the primary and secondary coils on a 6 volt CT90 ignition coil.  It's also a good idea to check your condenser while you have the coil assembly removed from your CT90 and I outlined how you can check your CT90 condenser at a post here at this link.

The coil in the picture below is from a 1969 CT90 I picked up recently.  To check the primary coil I set my meter at the lowest setting to measure ohms and then connect the leads from the meter to the ends of the red and green wires and look at the reading. For this coil the reading is 3.3 ohms which is a little higher then the 2.3 ohms that is used as an upper limit, but should be just fine and is understandable given the coil is 48 years old.

Here are some links to related posts:
How to Test Your CT90 Rectifier
CT90 Rectifier Upgrade

To check the secondary coil I first remove the plug cap as it may have a resister type so that it doesn't impact the reading and then I reset my meter to 30K ohms and connect one lead to either wire used in the primary coil test and the other lead to the wire at the core of the exposed end of the spark plug cable and then look at the reading.  For this coil the reading is 9.43K ohms which is good and is under the 10K ohm limit typically used.

Before I put the coil back into the bike I'll clean the coil frame as best I can to remove any corrosion and so that the is a good bond between the coil frame and the frame of the CT90.  If the spark plug cable is long enough I'll also clip off 1/4 to 1/2 inch so that the core of the cable is nice and tight that the spark plug cap screws into to help ensure a good connection. I also generally get a new spark plug cap if there is any question at all with the one that came on the bike as they are cheap and having a good solid spark depends on solid connections throughout the ignition system.

Links to Related Posts:
How to Test Your CT90 Rectifier
Basic Test of a CT90 Condenser
CT90 Rectifier Upgrade
Figuring out wire colors on a CT90 Stator when colors have faded or are not present

Helpful Links (Shop Manuals, Wire Diagram, Model Information, etc.)

Link to page with listing of CT90 parts available on Amazon


  1. THANK YOU! Clear pictures and easy to follow descriptions. Everywhere else I found instructions to do this made it seem like sorcery.

  2. Thank you tested ok 2.2 Ohms, 9.6 at 20K, Had to shorten the spark plug wire 1" to get spark at the plug end...
    Cleaned put back and out for a putt...

    Best regards, Roger


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