I would assume you would need to put a scope on it in circuit to see the signal. I don't know that you will read anything with it disconnected if the control line is an open collector type. That just means that the coil itself pulls the line high. I don't know how those work however so I am just guessing. I think you are on the right track though. It might be worth paying a good indy mechanic to check that, if you can find one. Very few are any good with electronics unfortunately.

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1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra