GM Service Manual Online
For 1990-2009 cars only
GEN F--Terminal Signal: The scan tool displays 0-100%. The scan tool displays 0-5% until the engine is running, then the percentage value varies depending on electrical loads.

GEN L--Terminal Signal: The scan tool displays Voltage/No Voltage. The scan tool displays Voltage until the engine is running, then displays No Voltage when the engine is running.

GEN L--Terminal Signal Command: The scan tool displays On/Off. The scan tool displays Off until the engine is running, at which time it will display On.

Ignition 1 Signal: The scan tool displays the current voltage at the battery.