Went to use it one morning and wouldn't start. Pulled the plug and no spark. No voltage to coil with ignition on. I don't have a manual so I don't know where I should be seeing voltage. Checked wires etc. There is a module inside the left rear wheel well as well as some other small black boxes directly under the front. It cranks over fine. Also checked the coil voltage while cranking and still nothing. I am checking the voltage at the coil at the positive side with the ground at the frame. Is there any other points to check?
My '88 is about same way. While cranking, moving key from on to off, it tries to start as key goes thru the half way mark between on & off. Does same thing moving kill switch same way. Creates a momentary spike but don't keep running. Was going to get ignition switch but beings kill switch does same, it must be one of the other components(coil or cdi)? Wondering, what is the "hall sensor" suggested below?
Worked on an '88 trx 300 this past spring with similar issues. If you could get it to start it would die suddenly and there would be no spark or voltage to the coil. I replaced the CDI box under the front plastics (approx $55) and its been great ever since. If you loosen the majority of the bolts on the front plastic you can just tilt it forward for easy access to the CDI box.
Testing a CDI is possible but it is done in OHMs You will need a Multi meter, manual or call the dealer to get the spec tolerances to your CDI unit, I could give you mine but they may be a diffrent range.
Just for the giggles you can bypass your key switch and kill switch (red Slide on the left bar) also check to make sure your not in Reverse you will not get spark in reverse