Setting base timing using a test light on TBI 350?

[Accelo]

Early ORBI GM distributors required a timing light to set the timing.
.You had to unplug a wire to the computer so it didn't take control of the timing.
I believe the wire, that had to be unplugged, was behind the glove-box. Been a long time so I am guessing on this one.
A timing light is connected to the battery, one 12V+ and one 12v-.
Then the third wire attaches to the #1 plug with. The clamp is inductive. No actual connection to the high voltage.