Check Engine Light/Self-Diagnostics Problem '89 300TE

The Check Engine light has been on for a while on my 89 300TE. I have to smog it this month to renew the California tabs, so I have to get
the light to turn off and fix whatever caused it. It has the 8 connector self-diagnostic unit with a push button and LED, some instructions I pulled out of On Demand made it look like it would be easy to get the failure codes but no luck so far. I push the buttton and hold it for various amounts of time, but the LED never flashes. I've tried it with Ignition off, Ignittion on engine stopped, and with engine running - nothing! I put an old analog multimeter between pins 1 and 3 with the ignition on, there is constant voltage, no fluctuation that would indicate impulses. The voltage turns off when the button is depressed. Anybody familiar with these Self-Diagnostics? Hopefully I'm overlooking something obvious.
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