The "on/off ratio" as you call it is called duty cycle. You can buy a digital voltmeter with a duty cycle function at Sears for 29.95. I happen to be in on a 10% off all Craftemen tools day and bought it for even less. It works great.
Most likely you will connect and find a 50% duty cycle. There are only a few other codes which may be trapped.
The pulsed codes are only on California vehicles for the models you listed.
Have a great day,